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authorFred Drake <fdrake@acm.org>1998-07-24 14:27:22 (GMT)
committerFred Drake <fdrake@acm.org>1998-07-24 14:27:22 (GMT)
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-\section{Built-in Types}
-\label{types}
+\section{Standard Module \module{types}}
+\declaremodule{standard}{types}
-The following sections describe the standard types that are built into
-the interpreter. These are the numeric types, sequence types, and
-several others, including types themselves. There is no explicit
-Boolean type; use integers instead.
-\indexii{built-in}{types}
-\indexii{Boolean}{type}
+\modulesynopsis{Names for all built-in types.}
-Some operations are supported by several object types; in particular,
-all objects can be compared, tested for truth value, and converted to
-a string (with the \code{`{\rm \ldots}`} notation). The latter conversion is
-implicitly used when an object is written by the \code{print} statement.
-\stindex{print}
-\subsection{Truth Value Testing}
-\label{truth}
+This module defines names for all object types that are used by the
+standard Python interpreter, but not for the types defined by various
+extension modules. It is safe to use \samp{from types import *} ---
+the module does not export any names besides the ones listed here.
+New names exported by future versions of this module will all end in
+\samp{Type}.
-Any object can be tested for truth value, for use in an \code{if} or
-\code{while} condition or as operand of the Boolean operations below.
-The following values are considered false:
-\stindex{if}
-\stindex{while}
-\indexii{truth}{value}
-\indexii{Boolean}{operations}
-\index{false}
-
-\setindexsubitem{(Built-in object)}
-\begin{itemize}
-
-\item \code{None}
- \ttindex{None}
-
-\item zero of any numeric type, e.g., \code{0}, \code{0L}, \code{0.0}.
-
-\item any empty sequence, e.g., \code{''}, \code{()}, \code{[]}.
-
-\item any empty mapping, e.g., \code{\{\}}.
-
-\item instances of user-defined classes, if the class defines a
- \code{__nonzero__()} or \code{__len__()} method, when that
- method returns zero.
-
-\end{itemize}
-
-All other values are considered true --- so objects of many types are
-always true.
-\index{true}
-
-Operations and built-in functions that have a Boolean result always
-return \code{0} for false and \code{1} for true, unless otherwise
-stated. (Important exception: the Boolean operations
-\samp{or}\opindex{or} and \samp{and}\opindex{and} always return one of
-their operands.)
-
-
-\subsection{Boolean Operations}
-\label{boolean}
-
-These are the Boolean operations, ordered by ascending priority:
-\indexii{Boolean}{operations}
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
- \lineiii{\var{x} or \var{y}}{if \var{x} is false, then \var{y}, else \var{x}}{(1)}
- \lineiii{\var{x} and \var{y}}{if \var{x} is false, then \var{x}, else \var{y}}{(1)}
- \hline
- \lineiii{not \var{x}}{if \var{x} is false, then \code{1}, else \code{0}}{(2)}
-\end{tableiii}
-\opindex{and}
-\opindex{or}
-\opindex{not}
-
-\noindent
-Notes:
-
-\begin{description}
-
-\item[(1)]
-These only evaluate their second argument if needed for their outcome.
-
-\item[(2)]
-\samp{not} has a lower priority than non-Boolean operators, so e.g.
-\code{not a == b} is interpreted as \code{not(a == b)}, and
-\code{a == not b} is a syntax error.
-
-\end{description}
-
-
-\subsection{Comparisons}
-\label{comparisons}
-
-Comparison operations are supported by all objects. They all have the
-same priority (which is higher than that of the Boolean operations).
-Comparisons can be chained arbitrarily, e.g. \code{x < y <= z} is
-equivalent to \code{x < y and y <= z}, except that \code{y} is
-evaluated only once (but in both cases \code{z} is not evaluated at
-all when \code{x < y} is found to be false).
-\indexii{chaining}{comparisons}
-
-This table summarizes the comparison operations:
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Meaning}{Notes}
- \lineiii{<}{strictly less than}{}
- \lineiii{<=}{less than or equal}{}
- \lineiii{>}{strictly greater than}{}
- \lineiii{>=}{greater than or equal}{}
- \lineiii{==}{equal}{}
- \lineiii{<>}{not equal}{(1)}
- \lineiii{!=}{not equal}{(1)}
- \lineiii{is}{object identity}{}
- \lineiii{is not}{negated object identity}{}
-\end{tableiii}
-\indexii{operator}{comparison}
-\opindex{==} % XXX *All* others have funny characters < ! >
-\opindex{is}
-\opindex{is not}
-
-\noindent
-Notes:
-
-\begin{description}
-
-\item[(1)]
-\code{<>} and \code{!=} are alternate spellings for the same operator.
-(I couldn't choose between \ABC{} and \C{}! :-)
-\index{ABC language@\ABC{} language}
-\index{language!ABC@\ABC{}}
-\indexii{C@\C{}}{language}
-
-\end{description}
-
-Objects of different types, except different numeric types, never
-compare equal; such objects are ordered consistently but arbitrarily
-(so that sorting a heterogeneous array yields a consistent result).
-Furthermore, some types (e.g., windows) support only a degenerate
-notion of comparison where any two objects of that type are unequal.
-Again, such objects are ordered arbitrarily but consistently.
-\indexii{types}{numeric}
-\indexii{objects}{comparing}
-
-(Implementation note: objects of different types except numbers are
-ordered by their type names; objects of the same types that don't
-support proper comparison are ordered by their address.)
-
-Two more operations with the same syntactic priority, \samp{in} and
-\samp{not in}, are supported only by sequence types (below).
-\opindex{in}
-\opindex{not in}
-
-
-\subsection{Numeric Types}
-\label{typesnumeric}
-
-There are four numeric types: \dfn{plain integers}, \dfn{long integers},
-\dfn{floating point numbers}, and \dfn{complex numbers}.
-Plain integers (also just called \dfn{integers})
-are implemented using \code{long} in \C{}, which gives them at least 32
-bits of precision. Long integers have unlimited precision. Floating
-point numbers are implemented using \code{double} in \C{}. All bets on
-their precision are off unless you happen to know the machine you are
-working with.
-\indexii{numeric}{types}
-\indexii{integer}{types}
-\indexii{integer}{type}
-\indexiii{long}{integer}{type}
-\indexii{floating point}{type}
-\indexii{complex number}{type}
-\indexii{C@\C{}}{language}
-
-Complex numbers have a real and imaginary part, which are both
-implemented using \code{double} in \C{}. To extract these parts from
-a complex number \var{z}, use \code{\var{z}.real} and \code{\var{z}.imag}.
-
-Numbers are created by numeric literals or as the result of built-in
-functions and operators. Unadorned integer literals (including hex
-and octal numbers) yield plain integers. Integer literals with an \samp{L}
-or \samp{l} suffix yield long integers
-(\samp{L} is preferred because \samp{1l} looks too much like eleven!).
-Numeric literals containing a decimal point or an exponent sign yield
-floating point numbers. Appending \samp{j} or \samp{J} to a numeric
-literal yields a complex number.
-\indexii{numeric}{literals}
-\indexii{integer}{literals}
-\indexiii{long}{integer}{literals}
-\indexii{floating point}{literals}
-\indexii{complex number}{literals}
-\indexii{hexadecimal}{literals}
-\indexii{octal}{literals}
-
-Python fully supports mixed arithmetic: when a binary arithmetic
-operator has operands of different numeric types, the operand with the
-``smaller'' type is converted to that of the other, where plain
-integer is smaller than long integer is smaller than floating point is
-smaller than complex.
-Comparisons between numbers of mixed type use the same rule.%
-\footnote{As a consequence, the list \code{[1, 2]} is considered equal
- to \code{[1.0, 2.0]}, and similar for tuples.}
-The functions \code{int()}, \code{long()}, \code{float()},
-and \code{complex()} can be used
-to coerce numbers to a specific type.
-\index{arithmetic}
-\bifuncindex{int}
-\bifuncindex{long}
-\bifuncindex{float}
-\bifuncindex{complex}
-
-All numeric types support the following operations, sorted by
-ascending priority (operations in the same box have the same
-priority; all numeric operations have a higher priority than
-comparison operations):
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
- \lineiii{\var{x} + \var{y}}{sum of \var{x} and \var{y}}{}
- \lineiii{\var{x} - \var{y}}{difference of \var{x} and \var{y}}{}
- \hline
- \lineiii{\var{x} * \var{y}}{product of \var{x} and \var{y}}{}
- \lineiii{\var{x} / \var{y}}{quotient of \var{x} and \var{y}}{(1)}
- \lineiii{\var{x} \%{} \var{y}}{remainder of \code{\var{x} / \var{y}}}{}
- \hline
- \lineiii{-\var{x}}{\var{x} negated}{}
- \lineiii{+\var{x}}{\var{x} unchanged}{}
- \hline
- \lineiii{abs(\var{x})}{absolute value or magnitude of \var{x}}{}
- \lineiii{int(\var{x})}{\var{x} converted to integer}{(2)}
- \lineiii{long(\var{x})}{\var{x} converted to long integer}{(2)}
- \lineiii{float(\var{x})}{\var{x} converted to floating point}{}
- \lineiii{complex(\var{re},\var{im})}{a complex number with real part \var{re}, imaginary part \var{im}. \var{im} defaults to zero.}{}
- \lineiii{divmod(\var{x}, \var{y})}{the pair \code{(\var{x} / \var{y}, \var{x} \%{} \var{y})}}{(3)}
- \lineiii{pow(\var{x}, \var{y})}{\var{x} to the power \var{y}}{}
- \lineiii{\var{x} ** \var{y}}{\var{x} to the power \var{y}}{}
-\end{tableiii}
-\indexiii{operations on}{numeric}{types}
-
-\noindent
-Notes:
-\begin{description}
-
-\item[(1)]
-For (plain or long) integer division, the result is an integer.
-The result is always rounded towards minus infinity: 1/2 is 0,
-(-1)/2 is -1, 1/(-2) is -1, and (-1)/(-2) is 0.
-\indexii{integer}{division}
-\indexiii{long}{integer}{division}
-
-\item[(2)]
-Conversion from floating point to (long or plain) integer may round or
-truncate as in \C{}; see functions \code{floor()} and \code{ceil()} in
-module \code{math} for well-defined conversions.
-\bifuncindex{floor}
-\bifuncindex{ceil}
-\indexii{numeric}{conversions}
-\refbimodindex{math}
-\indexii{C@\C{}}{language}
-
-\item[(3)]
-See the section on built-in functions for an exact definition.
-
-\end{description}
-% XXXJH exceptions: overflow (when? what operations?) zerodivision
-
-\subsubsection{Bit-string Operations on Integer Types}
-\nodename{Bit-string Operations}
-
-Plain and long integer types support additional operations that make
-sense only for bit-strings. Negative numbers are treated as their 2's
-complement value (for long integers, this assumes a sufficiently large
-number of bits that no overflow occurs during the operation).
-
-The priorities of the binary bit-wise operations are all lower than
-the numeric operations and higher than the comparisons; the unary
-operation \samp{\~} has the same priority as the other unary numeric
-operations (\samp{+} and \samp{-}).
-
-This table lists the bit-string operations sorted in ascending
-priority (operations in the same box have the same priority):
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
- \lineiii{\var{x} | \var{y}}{bitwise \dfn{or} of \var{x} and \var{y}}{}
- \lineiii{\var{x} \^{} \var{y}}{bitwise \dfn{exclusive or} of \var{x} and \var{y}}{}
- \lineiii{\var{x} \&{} \var{y}}{bitwise \dfn{and} of \var{x} and \var{y}}{}
- \lineiii{\var{x} << \var{n}}{\var{x} shifted left by \var{n} bits}{(1), (2)}
- \lineiii{\var{x} >> \var{n}}{\var{x} shifted right by \var{n} bits}{(1), (3)}
- \hline
- \lineiii{\~\var{x}}{the bits of \var{x} inverted}{}
-\end{tableiii}
-\indexiii{operations on}{integer}{types}
-\indexii{bit-string}{operations}
-\indexii{shifting}{operations}
-\indexii{masking}{operations}
-
-\noindent
-Notes:
-\begin{description}
-\item[(1)] Negative shift counts are illegal and cause a
-\exception{ValueError} to be raised.
-\item[(2)] A left shift by \var{n} bits is equivalent to
-multiplication by \code{pow(2, \var{n})} without overflow check.
-\item[(3)] A right shift by \var{n} bits is equivalent to
-division by \code{pow(2, \var{n})} without overflow check.
-\end{description}
-
-
-\subsection{Sequence Types}
-\label{typesseq}
-
-There are three sequence types: strings, lists and tuples.
-
-Strings literals are written in single or double quotes:
-\code{'xyzzy'}, \code{"frobozz"}. See Chapter 2 of the \emph{Python
-Reference Manual} for more about string literals. Lists are
-constructed with square brackets, separating items with commas:
-\code{[a, b, c]}. Tuples are constructed by the comma operator (not
-within square brackets), with or without enclosing parentheses, but an
-empty tuple must have the enclosing parentheses, e.g.,
-\code{a, b, c} or \code{()}. A single item tuple must have a trailing
-comma, e.g., \code{(d,)}.
-\indexii{sequence}{types}
-\indexii{string}{type}
-\indexii{tuple}{type}
-\indexii{list}{type}
-
-Sequence types support the following operations. The \samp{in} and
-\samp{not in} operations have the same priorities as the comparison
-operations. The \samp{+} and \samp{*} operations have the same
-priority as the corresponding numeric operations.\footnote{They must
-have since the parser can't tell the type of the operands.}
-
-This table lists the sequence operations sorted in ascending priority
-(operations in the same box have the same priority). In the table,
-\var{s} and \var{t} are sequences of the same type; \var{n}, \var{i}
-and \var{j} are integers:
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
- \lineiii{\var{x} in \var{s}}{\code{1} if an item of \var{s} is equal to \var{x}, else \code{0}}{}
- \lineiii{\var{x} not in \var{s}}{\code{0} if an item of \var{s} is
-equal to \var{x}, else \code{1}}{}
- \hline
- \lineiii{\var{s} + \var{t}}{the concatenation of \var{s} and \var{t}}{}
- \lineiii{\var{s} * \var{n}{\rm ,} \var{n} * \var{s}}{\var{n} copies of \var{s} concatenated}{(3)}
- \hline
- \lineiii{\var{s}[\var{i}]}{\var{i}'th item of \var{s}, origin 0}{(1)}
- \lineiii{\var{s}[\var{i}:\var{j}]}{slice of \var{s} from \var{i} to \var{j}}{(1), (2)}
- \hline
- \lineiii{len(\var{s})}{length of \var{s}}{}
- \lineiii{min(\var{s})}{smallest item of \var{s}}{}
- \lineiii{max(\var{s})}{largest item of \var{s}}{}
-\end{tableiii}
-\indexiii{operations on}{sequence}{types}
-\bifuncindex{len}
-\bifuncindex{min}
-\bifuncindex{max}
-\indexii{concatenation}{operation}
-\indexii{repetition}{operation}
-\indexii{subscript}{operation}
-\indexii{slice}{operation}
-\opindex{in}
-\opindex{not in}
-
-\noindent
-Notes:
-
-\begin{description}
-
-\item[(1)] If \var{i} or \var{j} is negative, the index is relative to
- the end of the string, i.e., \code{len(\var{s}) + \var{i}} or
- \code{len(\var{s}) + \var{j}} is substituted. But note that \code{-0} is
- still \code{0}.
-
-\item[(2)] The slice of \var{s} from \var{i} to \var{j} is defined as
- the sequence of items with index \var{k} such that \code{\var{i} <=
- \var{k} < \var{j}}. If \var{i} or \var{j} is greater than
- \code{len(\var{s})}, use \code{len(\var{s})}. If \var{i} is omitted,
- use \code{0}. If \var{j} is omitted, use \code{len(\var{s})}. If
- \var{i} is greater than or equal to \var{j}, the slice is empty.
-
-\item[(3)] Values of \var{n} less than \code{0} are treated as
- \code{0} (which yields an empty sequence of the same type as
- \var{s}).
-
-\end{description}
-
-\subsubsection{More String Operations}
-
-String objects have one unique built-in operation: the \code{\%}
-operator (modulo) with a string left argument interprets this string
-as a \C{} \cfunction{sprintf()} format string to be applied to the
-right argument, and returns the string resulting from this formatting
-operation.
-
-The right argument should be a tuple with one item for each argument
-required by the format string; if the string requires a single
-argument, the right argument may also be a single non-tuple object.%
-\footnote{A tuple object in this case should be a singleton.}
-The following format characters are understood:
-\code{\%}, \code{c}, \code{s}, \code{i}, \code{d}, \code{u}, \code{o},
-\code{x}, \code{X}, \code{e}, \code{E}, \code{f}, \code{g}, \code{G}.
-Width and precision may be a \code{*} to specify that an integer argument
-specifies the actual width or precision. The flag characters
-\code{-}, \code{+}, blank, \code{\#} and \code{0} are understood. The
-size specifiers \code{h}, \code{l} or \code{L} may be
-present but are ignored. The \code{\%s} conversion takes any Python
-object and converts it to a string using \code{str()} before
-formatting it. The ANSI features \code{\%p} and \code{\%n}
-are not supported. Since Python strings have an explicit length,
-\code{\%s} conversions don't assume that \code{'\e0'} is the end of
-the string.
-
-For safety reasons, floating point precisions are clipped to 50;
-\code{\%f} conversions for numbers whose absolute value is over 1e25
-are replaced by \code{\%g} conversions.%
-\footnote{These numbers are fairly arbitrary. They are intended to
-avoid printing endless strings of meaningless digits without hampering
-correct use and without having to know the exact precision of floating
-point values on a particular machine.}
-All other errors raise exceptions.
-
-If the right argument is a dictionary (or any kind of mapping), then
-the formats in the string must have a parenthesized key into that
-dictionary inserted immediately after the \character{\%} character,
-and each format formats the corresponding entry from the mapping.
-For example:
+Typical use is for functions that do different things depending on
+their argument types, like the following:
\begin{verbatim}
->>> count = 2
->>> language = 'Python'
->>> print '%(language)s has %(count)03d quote types.' % vars()
-Python has 002 quote types.
+from types import *
+def delete(list, item):
+ if type(item) is IntType:
+ del list[item]
+ else:
+ list.remove(item)
\end{verbatim}
-In this case no \code{*} specifiers may occur in a format (since they
-require a sequential parameter list).
-
-Additional string operations are defined in standard module
-\module{string} and in built-in module \module{re}.
-\refstmodindex{string}
-\refbimodindex{re}
-
-\subsubsection{Mutable Sequence Types}
-
-List objects support additional operations that allow in-place
-modification of the object.
-These operations would be supported by other mutable sequence types
-(when added to the language) as well.
-Strings and tuples are immutable sequence types and such objects cannot
-be modified once created.
-The following operations are defined on mutable sequence types (where
-\var{x} is an arbitrary object):
-\indexiii{mutable}{sequence}{types}
-\indexii{list}{type}
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
- \lineiii{\var{s}[\var{i}] = \var{x}}
- {item \var{i} of \var{s} is replaced by \var{x}}{}
- \lineiii{\var{s}[\var{i}:\var{j}] = \var{t}}
- {slice of \var{s} from \var{i} to \var{j} is replaced by \var{t}}{}
- \lineiii{del \var{s}[\var{i}:\var{j}]}
- {same as \code{\var{s}[\var{i}:\var{j}] = []}}{}
- \lineiii{\var{s}.append(\var{x})}
- {same as \code{\var{s}[len(\var{s}):len(\var{s})] = [\var{x}]}}{}
- \lineiii{\var{s}.count(\var{x})}
- {return number of \var{i}'s for which \code{\var{s}[\var{i}] == \var{x}}}{}
- \lineiii{\var{s}.index(\var{x})}
- {return smallest \var{i} such that \code{\var{s}[\var{i}] == \var{x}}}{(1)}
- \lineiii{\var{s}.insert(\var{i}, \var{x})}
- {same as \code{\var{s}[\var{i}:\var{i}] = [\var{x}]}
- if \code{\var{i} >= 0}}{}
- \lineiii{\var{s}.pop(\optional{\var{i}})}
- {same as \code{\var{x} = \var{s}[\var{i}]; del \var{s}[\var{i}]; return \var{x}}}{(4)}
- \lineiii{\var{s}.remove(\var{x})}
- {same as \code{del \var{s}[\var{s}.index(\var{x})]}}{(1)}
- \lineiii{\var{s}.reverse()}
- {reverses the items of \var{s} in place}{(3)}
- \lineiii{\var{s}.sort(\optional{\var{cmpfunc}})}
- {sort the items of \var{s} in place}{(2), (3)}
-\end{tableiii}
-\indexiv{operations on}{mutable}{sequence}{types}
-\indexiii{operations on}{sequence}{types}
-\indexiii{operations on}{list}{type}
-\indexii{subscript}{assignment}
-\indexii{slice}{assignment}
-\stindex{del}
-\setindexsubitem{(list method)}
-\ttindex{append}
-\ttindex{count}
-\ttindex{index}
-\ttindex{insert}
-\ttindex{pop}
-\ttindex{remove}
-\ttindex{reverse}
-\ttindex{sort}
-
-\noindent
-Notes:
-\begin{description}
-\item[(1)] Raises an exception when \var{x} is not found in \var{s}.
-
-\item[(2)] The \code{sort()} method takes an optional argument
- specifying a comparison function of two arguments (list items) which
- should return \code{-1}, \code{0} or \code{1} depending on whether the
- first argument is considered smaller than, equal to, or larger than the
- second argument. Note that this slows the sorting process down
- considerably; e.g. to sort a list in reverse order it is much faster
- to use calls to \code{sort()} and \code{reverse()} than to use
- \code{sort()} with a comparison function that reverses the ordering of
- the elements.
-
-\item[(3)] The \code{sort()} and \code{reverse()} methods modify the
-list in place for economy of space when sorting or reversing a large
-list. They don't return the sorted or reversed list to remind you of
-this side effect.
-
-\item[(4)] The \method{pop()} method is experimental and not supported
-by other mutable sequence types than lists.
-The optional argument \var{i} defaults to \code{-1}, so that
-by default the last item is removed and returned.
-
-\end{description}
-
-
-\subsection{Mapping Types}
-\label{typesmapping}
-
-A \dfn{mapping} object maps values of one type (the key type) to
-arbitrary objects. Mappings are mutable objects. There is currently
-only one standard mapping type, the \dfn{dictionary}. A dictionary's keys are
-almost arbitrary values. The only types of values not acceptable as
-keys are values containing lists or dictionaries or other mutable
-types that are compared by value rather than by object identity.
-Numeric types used for keys obey the normal rules for numeric
-comparison: if two numbers compare equal (e.g. \code{1} and
-\code{1.0}) then they can be used interchangeably to index the same
-dictionary entry.
-
-\indexii{mapping}{types}
-\indexii{dictionary}{type}
-
-Dictionaries are created by placing a comma-separated list of
-\code{\var{key}: \var{value}} pairs within braces, for example:
-\code{\{'jack': 4098, 'sjoerd': 4127\}} or
-\code{\{4098: 'jack', 4127: 'sjoerd'\}}.
-
-The following operations are defined on mappings (where \var{a} is a
-mapping, \var{k} is a key and \var{x} is an arbitrary object):
-
-\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
- \lineiii{len(\var{a})}{the number of items in \var{a}}{}
- \lineiii{\var{a}[\var{k}]}{the item of \var{a} with key \var{k}}{(1)}
- \lineiii{\var{a}[\var{k}] = \var{x}}{set \code{\var{a}[\var{k}]} to \var{x}}{}
- \lineiii{del \var{a}[\var{k}]}{remove \code{\var{a}[\var{k}]} from \var{a}}{(1)}
- \lineiii{\var{a}.clear()}{remove all items from \code{a}}{}
- \lineiii{\var{a}.copy()}{a (shallow) copy of \code{a}}{}
- \lineiii{\var{a}.has_key(\var{k})}{\code{1} if \var{a} has a key \var{k}, else \code{0}}{}
- \lineiii{\var{a}.items()}{a copy of \var{a}'s list of (key, item) pairs}{(2)}
- \lineiii{\var{a}.keys()}{a copy of \var{a}'s list of keys}{(2)}
- \lineiii{\var{a}.update(\var{b})}{\code{for k, v in \var{b}.items(): \var{a}[k] = v}}{(3)}
- \lineiii{\var{a}.values()}{a copy of \var{a}'s list of values}{(2)}
- \lineiii{\var{a}.get(\var{k}\optional{, \var{f}})}{the item of \var{a} with key \var{k}}{(4)}
-\end{tableiii}
-\indexiii{operations on}{mapping}{types}
-\indexiii{operations on}{dictionary}{type}
-\stindex{del}
-\bifuncindex{len}
-\setindexsubitem{(dictionary method)}
-\ttindex{keys}
-\ttindex{has_key}
-
-\noindent
-Notes:
-\begin{description}
-\item[(1)] Raises an exception if \var{k} is not in the map.
-
-\item[(2)] Keys and values are listed in random order.
-
-\item[(3)] \var{b} must be of the same type as \var{a}.
-
-\item[(4)] Never raises an exception if \var{k} is not in the map,
-instead it returns \var{f}. \var{f} is optional, when not provided
-and \var{k} is not in the map, \code{None} is returned.
-\end{description}
-
-
-\subsection{Other Built-in Types}
-\label{typesother}
-
-The interpreter supports several other kinds of objects.
-Most of these support only one or two operations.
-
-\subsubsection{Modules}
-
-The only special operation on a module is attribute access:
-\code{\var{m}.\var{name}}, where \var{m} is a module and \var{name}
-accesses a name defined in \var{m}'s symbol table. Module attributes
-can be assigned to. (Note that the \code{import} statement is not,
-strictly spoking, an operation on a module object; \code{import
-\var{foo}} does not require a module object named \var{foo} to exist,
-rather it requires an (external) \emph{definition} for a module named
-\var{foo} somewhere.)
-
-A special member of every module is \code{__dict__}.
-This is the dictionary containing the module's symbol table.
-Modifying this dictionary will actually change the module's symbol
-table, but direct assignment to the \code{__dict__} attribute is not
-possible (i.e., you can write \code{\var{m}.__dict__['a'] = 1}, which
-defines \code{\var{m}.a} to be \code{1}, but you can't write
-\code{\var{m}.__dict__ = \{\}}.
-
-Modules are written like this: \code{<module 'sys'>}.
-
-\subsubsection{Classes and Class Instances}
-\nodename{Classes and Instances}
-
-See Chapters 3 and 7 of the \emph{Python Reference Manual} for these.
-
-\subsubsection{Functions}
-
-Function objects are created by function definitions. The only
-operation on a function object is to call it:
-\code{\var{func}(\var{argument-list})}.
-
-There are really two flavors of function objects: built-in functions
-and user-defined functions. Both support the same operation (to call
-the function), but the implementation is different, hence the
-different object types.
-
-The implementation adds two special read-only attributes:
-\code{\var{f}.func_code} is a function's \dfn{code
-object}\obindex{code} (see below) and \code{\var{f}.func_globals} is
-the dictionary used as the function's global name space (this is the
-same as \code{\var{m}.__dict__} where \var{m} is the module in which
-the function \var{f} was defined).
-
-
-\subsubsection{Methods}
-\obindex{method}
-
-Methods are functions that are called using the attribute notation.
-There are two flavors: built-in methods (such as \code{append()} on
-lists) and class instance methods. Built-in methods are described
-with the types that support them.
-
-The implementation adds two special read-only attributes to class
-instance methods: \code{\var{m}.im_self} is the object whose method this
-is, and \code{\var{m}.im_func} is the function implementing the method.
-Calling \code{\var{m}(\var{arg-1}, \var{arg-2}, {\rm \ldots},
-\var{arg-n})} is completely equivalent to calling
-\code{\var{m}.im_func(\var{m}.im_self, \var{arg-1}, \var{arg-2}, {\rm
-\ldots}, \var{arg-n})}.
-
-See the \emph{Python Reference Manual} for more information.
-
-\subsubsection{Code Objects}
-\obindex{code}
-
-Code objects are used by the implementation to represent
-``pseudo-compiled'' executable Python code such as a function body.
-They differ from function objects because they don't contain a
-reference to their global execution environment. Code objects are
-returned by the built-in \code{compile()} function and can be
-extracted from function objects through their \code{func_code}
-attribute.
-\bifuncindex{compile}
-\ttindex{func_code}
-
-A code object can be executed or evaluated by passing it (instead of a
-source string) to the \code{exec} statement or the built-in
-\code{eval()} function.
-\stindex{exec}
-\bifuncindex{eval}
-
-See the \emph{Python Reference Manual} for more information.
-
-\subsubsection{Type Objects}
-\label{bltin-type-objects}
-
-Type objects represent the various object types. An object's type is
-accessed by the built-in function \code{type()}. There are no special
-operations on types. The standard module \code{types} defines names
-for all standard built-in types.
-\bifuncindex{type}
-\refstmodindex{types}
-
-Types are written like this: \code{<type 'int'>}.
-
-\subsubsection{The Null Object}
-\label{bltin-null-object}
-
-This object is returned by functions that don't explicitly return a
-value. It supports no special operations. There is exactly one null
-object, named \code{None} (a built-in name).
-
-It is written as \code{None}.
-
-\subsubsection{File Objects}
-\label{bltin-file-objects}
-
-File objects are implemented using \C{}'s \code{stdio} package and can be
-created with the built-in function \code{open()} described under
-Built-in Functions below. They are also returned by some other
-built-in functions and methods, e.g.\ \code{posix.popen()} and
-\code{posix.fdopen()} and the \code{makefile()} method of socket
-objects.
-\bifuncindex{open}
-\refbimodindex{posix}
-\refbimodindex{socket}
-
-When a file operation fails for an I/O-related reason, the exception
-\code{IOError} is raised. This includes situations where the
-operation is not defined for some reason, like \code{seek()} on a tty
-device or writing a file opened for reading.
-
-Files have the following methods:
-
-
-\begin{methoddesc}[file]{close}{}
- Close the file. A closed file cannot be read or written anymore.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{flush}{}
- Flush the internal buffer, like \code{stdio}'s \code{fflush()}.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{isatty}{}
- Return \code{1} if the file is connected to a tty(-like) device, else
- \code{0}.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{fileno}{}
-Return the integer ``file descriptor'' that is used by the underlying
-implementation to request I/O operations from the operating system.
-This can be useful for other, lower level interfaces that use file
-descriptors, e.g. module \code{fcntl} or \code{os.read()} and friends.
-\refbimodindex{fcntl}
-\end{methoddesc}
-
-\begin{methoddesc}[file]{read}{\optional{size}}
- Read at most \var{size} bytes from the file (less if the read hits
- \EOF{} or no more data is immediately available on a pipe, tty or
- similar device). If the \var{size} argument is negative or omitted,
- read all data until \EOF{} is reached. The bytes are returned as a string
- object. An empty string is returned when \EOF{} is encountered
- immediately. (For certain files, like ttys, it makes sense to
- continue reading after an \EOF{} is hit.)
-\end{methoddesc}
-
-\begin{methoddesc}[file]{readline}{\optional{size}}
- Read one entire line from the file. A trailing newline character is
- kept in the string%
-\footnote{The advantage of leaving the newline on is that an empty string
- can be returned to mean \EOF{} without being ambiguous. Another
- advantage is that (in cases where it might matter, e.g. if you
- want to make an exact copy of a file while scanning its lines)
- you can tell whether the last line of a file ended in a newline
- or not (yes this happens!).}
- (but may be absent when a file ends with an
- incomplete line). If the \var{size} argument is present and
- non-negative, it is a maximum byte count (including the trailing
- newline) and an incomplete line may be returned.
- An empty string is returned when \EOF{} is hit
- immediately. Note: unlike \code{stdio}'s \cfunction{fgets()}, the returned
- string contains null characters (\code{'\e 0'}) if they occurred in the
- input.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{readlines}{\optional{sizehint}}
- Read until \EOF{} using \method{readline()} and return a list containing
- the lines thus read. If the optional \var{sizehint} argument is
- present, instead of reading up to \EOF{}, whole lines totalling
- approximately \var{sizehint} bytes (possibly after rounding up to an
- internal buffer size) are read.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{seek}{offset\optional{, whence}}
- Set the file's current position, like \code{stdio}'s \cfunction{fseek()}.
- The \var{whence} argument is optional and defaults to \code{0}
- (absolute file positioning); other values are \code{1} (seek
- relative to the current position) and \code{2} (seek relative to the
- file's end). There is no return value.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{tell}{}
- Return the file's current position, like \code{stdio}'s
- \cfunction{ftell()}.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{truncate}{\optional{size}}
-Truncate the file's size. If the optional size argument present, the
-file is truncated to (at most) that size. The size defaults to the
-current position. Availability of this function depends on the
-operating system version (e.g., not all \UNIX{} versions support this
-operation).
-\end{methoddesc}
-
-\begin{methoddesc}[file]{write}{str}
-Write a string to the file. There is no return value. Note: due to
-buffering, the string may not actually show up in the file until
-the \method{flush()} or \method{close()} method is called.
-\end{methoddesc}
-
-\begin{methoddesc}[file]{writelines}{list}
-Write a list of strings to the file. There is no return value.
-(The name is intended to match \method{readlines()};
-\method{writelines()} does not add line separators.)
-\end{methoddesc}
-
-
-File objects also offer the following attributes:
-
-\begin{memberdesc}[file]{closed}
-Boolean indicating the current state of the file object. This is a
-read-only attribute; the \method{close()} method changes the value.
-\end{memberdesc}
-
-\begin{memberdesc}[file]{mode}
-The I/O mode for the file. If the file was created using the
-\function{open()} built-in function, this will be the value of the
-\var{mode} parameter. This is a read-only attribute.
-\end{memberdesc}
-
-\begin{memberdesc}[file]{name}
-If the file object was created using \function{open()}, the name of
-the file. Otherwise, some string that indicates the source of the
-file object, of the form \samp{<\mbox{\ldots}>}. This is a read-only
-attribute.
-\end{memberdesc}
-
-\begin{memberdesc}[file]{softspace}
-Boolean that indicates whether a space character needs to be printed
-before another value when using the \keyword{print} statement.
-Classes that are trying to simulate a file object should also have a
-writable \member{softspace} attribute, which should be initialized to
-zero. This will be automatic for classes implemented in Python; types
-implemented in \C{} will have to provide a writable \member{softspace}
-attribute.
-\end{memberdesc}
-
-\subsubsection{Internal Objects}
-
-See the \emph{Python Reference Manual} for this information. It
-describes code objects, stack frame objects, traceback objects, and
-slice objects.
-
-
-\subsection{Special Attributes}
-\label{specialattrs}
-
-The implementation adds a few special read-only attributes to several
-object types, where they are relevant:
-
-\begin{itemize}
-
-\item
-\code{\var{x}.__dict__} is a dictionary of some sort used to store an
-object's (writable) attributes;
-
-\item
-\code{\var{x}.__methods__} lists the methods of many built-in object types,
-e.g., \code{[].__methods__} yields
-\code{['append', 'count', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']};
-
-\item
-\code{\var{x}.__members__} lists data attributes;
-
-\item
-\code{\var{x}.__class__} is the class to which a class instance belongs;
-
-\item
-\code{\var{x}.__bases__} is the tuple of base classes of a class object.
+The module defines the following names:
-\end{itemize}
+\begin{datadesc}{NoneType}
+The type of \code{None}.
+\end{datadesc}
+
+\begin{datadesc}{TypeType}
+The type of type objects (such as returned by
+\function{type()}\bifuncindex{type}).
+\end{datadesc}
+
+\begin{datadesc}{IntType}
+The type of integers (e.g. \code{1}).
+\end{datadesc}
+
+\begin{datadesc}{LongType}
+The type of long integers (e.g. \code{1L}).
+\end{datadesc}
+
+\begin{datadesc}{FloatType}
+The type of floating point numbers (e.g. \code{1.0}).
+\end{datadesc}
+
+\begin{datadesc}{StringType}
+The type of character strings (e.g. \code{'Spam'}).
+\end{datadesc}
+
+\begin{datadesc}{TupleType}
+The type of tuples (e.g. \code{(1, 2, 3, 'Spam')}).
+\end{datadesc}
+
+\begin{datadesc}{ListType}
+The type of lists (e.g. \code{[0, 1, 2, 3]}).
+\end{datadesc}
+
+\begin{datadesc}{DictType}
+The type of dictionaries (e.g. \code{\{'Bacon': 1, 'Ham': 0\}}).
+\end{datadesc}
+
+\begin{datadesc}{DictionaryType}
+An alternate name for \code{DictType}.
+\end{datadesc}
+
+\begin{datadesc}{FunctionType}
+The type of user-defined functions and lambdas.
+\end{datadesc}
+
+\begin{datadesc}{LambdaType}
+An alternate name for \code{FunctionType}.
+\end{datadesc}
+
+\begin{datadesc}{CodeType}
+The type for code objects such as returned by
+\function{compile()}\bifuncindex{compile}.
+\end{datadesc}
+
+\begin{datadesc}{ClassType}
+The type of user-defined classes.
+\end{datadesc}
+
+\begin{datadesc}{InstanceType}
+The type of instances of user-defined classes.
+\end{datadesc}
+
+\begin{datadesc}{MethodType}
+The type of methods of user-defined class instances.
+\end{datadesc}
+
+\begin{datadesc}{UnboundMethodType}
+An alternate name for \code{MethodType}.
+\end{datadesc}
+
+\begin{datadesc}{BuiltinFunctionType}
+The type of built-in functions like \function{len()} or
+\function{sys.exit()}.
+\end{datadesc}
+
+\begin{datadesc}{BuiltinMethodType}
+An alternate name for \code{BuiltinFunction}.
+\end{datadesc}
+
+\begin{datadesc}{ModuleType}
+The type of modules.
+\end{datadesc}
+
+\begin{datadesc}{FileType}
+The type of open file objects such as \code{sys.stdout}.
+\end{datadesc}
+
+\begin{datadesc}{XRangeType}
+The type of range objects returned by
+\function{xrange()}\bifuncindex{xrange}.
+\end{datadesc}
+
+\begin{datadesc}{TracebackType}
+The type of traceback objects such as found in
+\code{sys.exc_traceback}.
+\end{datadesc}
+
+\begin{datadesc}{FrameType}
+The type of frame objects such as found in \code{tb.tb_frame} if
+\code{tb} is a traceback object.
+\end{datadesc}