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diff --git a/Doc/lib/libfuncs.tex b/Doc/lib/libfuncs.tex new file mode 100644 index 0000000..e0b36f3 --- /dev/null +++ b/Doc/lib/libfuncs.tex @@ -0,0 +1,356 @@ +\section{Built-in Functions} + +The Python interpreter has a number of functions built into it that +are always available. They are listed here in alphabetical order. + + +\renewcommand{\indexsubitem}{(built-in function)} +\begin{funcdesc}{abs}{x} + Return the absolute value of a number. The argument may be a plain + or long integer or a floating point number. +\end{funcdesc} + +\begin{funcdesc}{apply}{function\, args} +The \var{function} argument must be a callable object (a user-defined or +built-in function or method, or a class object) and the \var{args} +argument must be a tuple. The \var{function} is called with +\var{args} as argument list; the number of arguments is the the length +of the tuple. (This is different from just calling +\code{\var{func}(\var{args})}, since in that case there is always +exactly one argument.) +\end{funcdesc} + +\begin{funcdesc}{chr}{i} + Return a string of one character whose \ASCII{} code is the integer + \var{i}, e.g., \code{chr(97)} returns the string \code{'a'}. This is the + inverse of \code{ord()}. The argument must be in the range [0..255], + inclusive. +\end{funcdesc} + +\begin{funcdesc}{cmp}{x\, y} + Compare the two objects \var{x} and \var{y} and return an integer + according to the outcome. The return value is negative if \code{\var{x} + < \var{y}}, zero if \code{\var{x} == \var{y}} and strictly positive if + \code{\var{x} > \var{y}}. +\end{funcdesc} + +\begin{funcdesc}{coerce}{x\, y} + Return a tuple consisting of the two numeric arguments converted to + a common type, using the same rules as used by arithmetic + operations. +\end{funcdesc} + +\begin{funcdesc}{compile}{string\, filename\, kind} + Compile the \var{string} into a code object. Code objects can be + executed by a \code{exec()} statement or evaluated by a call to + \code{eval()}. The \var{filename} argument should + give the file from which the code was read; pass e.g. \code{'<string>'} + if it wasn't read from a file. The \var{kind} argument specifies + what kind of code must be compiled; it can be \code{'exec'} if + \var{string} consists of a sequence of statements, or \code{'eval'} + if it consists of a single expression. +\end{funcdesc} + +\begin{funcdesc}{dir}{} + Without arguments, return the list of names in the current local + symbol table. With a module, class or class instance object as + argument (or anything else that has a \code{__dict__} attribute), + returns the list of names in that object's attribute dictionary. + The resulting list is sorted. For example: + +\bcode\begin{verbatim} +>>> import sys +>>> dir() +['sys'] +>>> dir(sys) +['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'] +>>> +\end{verbatim}\ecode +\end{funcdesc} + +\begin{funcdesc}{divmod}{a\, b} + Take two numbers as arguments and return a pair of integers + consisting of their integer quotient and remainder. With mixed + operand types, the rules for binary arithmetic operators apply. For + plain and long integers, the result is the same as + \code{(\var{a} / \var{b}, \var{a} \%{} \var{b})}. + For floating point numbers the result is the same as + \code{(math.floor(\var{a} / \var{b}), \var{a} \%{} \var{b})}. +\end{funcdesc} + +\begin{funcdesc}{eval}{s\, globals\, locals} + The arguments are a string and two optional dictionaries. The + string argument is parsed and evaluated as a Python expression + (technically speaking, a condition list) using the dictionaries as + global and local name space. The string must not contain null bytes + or newline characters. The return value is the + result of the expression. If the third argument is omitted it + defaults to the second. If both dictionaries are omitted, the + expression is executed in the environment where \code{eval} is + called. Syntax errors are reported as exceptions. Example: + +\bcode\begin{verbatim} +>>> x = 1 +>>> print eval('x+1') +2 +>>> +\end{verbatim}\ecode + + This function can also be used to execute arbitrary code objects + (e.g. created by \code{compile()}). In this case pass a code + object instead of a string. The code object must have been compiled + passing \code{'eval'} to the \var{kind} argument. + + Note: dynamic execution of statements is supported by the + \code{exec} statement. + +\end{funcdesc} + +\begin{funcdesc}{filter}{function\, list} +Construct a list from those elements of \var{list} for which +\var{function} returns true. If \var{list} is a string or a tuple, +the result also has that type; otherwise it is always a list. If +\var{function} is \code{None}, the identity function is assumed, +i.e. all elements of \var{list} that are false (zero or empty) are +removed. +\end{funcdesc} + +\begin{funcdesc}{float}{x} + Convert a number to floating point. The argument may be a plain or + long integer or a floating point number. +\end{funcdesc} + +\begin{funcdesc}{getattr}{object\, name} + The arguments are an object and a string. The string must be the + name + of one of the object's attributes. The result is the value of that + attribute. For example, \code{getattr(\var{x}, '\var{foobar}')} is equivalent to + \code{\var{x}.\var{foobar}}. +\end{funcdesc} + +\begin{funcdesc}{hasattr}{object\, name} + The arguments are an object and a string. The result is 1 if the + string is the name of one of the object's attributes, 0 if not. + (This is implemented by calling \code{getattr(object, name)} and + seeing whether it raises an exception or not.) +\end{funcdesc} + +\begin{funcdesc}{hash}{object} + Return the hash value of the object (if it has one). Hash values + are 32-bit integers. They are used to quickly compare dictionary + keys during a dictionary lookup. Numeric values that compare equal + have the same hash value (even if they are of different types, e.g. + 1 and 1.0). +\end{funcdesc} + +\begin{funcdesc}{hex}{x} + Convert a number to a hexadecimal string. The result is a valid + Python expression. +\end{funcdesc} + +\begin{funcdesc}{id}{object} + Return the `identity' of an object. This is an integer which is + guaranteed to be unique and constant for this object during its + lifetime. (Two objects whose lifetimes are disjunct may have the + same id() value.) (Implementation note: this is the address of the + object.) +\end{funcdesc} + +\begin{funcdesc}{input}{prompt} + Almost equivalent to \code{eval(raw_input(\var{prompt}))}. As for + \code{raw_input()}, the prompt argument is optional. The difference is + that a long input expression may be broken over multiple lines using the + backslash convention. +\end{funcdesc} + +\begin{funcdesc}{int}{x} + Convert a number to a plain integer. The argument may be a plain or + long integer or a floating point number. +\end{funcdesc} + +\begin{funcdesc}{len}{s} + Return the length (the number of items) of an object. The argument + may be a sequence (string, tuple or list) or a mapping (dictionary). +\end{funcdesc} + +\begin{funcdesc}{long}{x} + Convert a number to a long integer. The argument may be a plain or + long integer or a floating point number. +\end{funcdesc} + +\begin{funcdesc}{map}{function\, list\, ...} +Apply \var{function} to every item of \var{list} and return a list +of the results. If additional \var{list} arguments are passed, +\var{function} must take that many arguments and is applied to +the items of all lists in parallel; if a list is shorter than another +it is assumed to be extended with \code{None} items. If +\var{function} is \code{None}, the identity function is assumed; if +there are multiple list arguments, \code{map} returns a list +consisting of tuples containing the corresponding items from all lists +(i.e. a kind of transpose operation). The \var{list} arguments may be +any kind of sequence; the result is always a list. +\end{funcdesc} + +\begin{funcdesc}{max}{s} + Return the largest item of a non-empty sequence (string, tuple or + list). +\end{funcdesc} + +\begin{funcdesc}{min}{s} + Return the smallest item of a non-empty sequence (string, tuple or + list). +\end{funcdesc} + +\begin{funcdesc}{oct}{x} + Convert a number to an octal string. The result is a valid Python + expression. +\end{funcdesc} + +\begin{funcdesc}{open}{filename\, mode} + % XXXJH xrefs here to Built-in types? + Return a new file object (described earlier under Built-in Types). + The string arguments are the same as for \code{stdio}'s + \code{fopen()}: \var{filename} is the file name to be opened, + \var{mode} indicates how the file is to be opened: \code{'r'} for + reading, \code{'w'} for writing (truncating an existing file), and + \code{'a'} opens it for appending. Modes \code{'r+'}, \code{'w+'} and + \code{'a+'} open the file for updating, provided the underlying + \code{stdio} library understands this. On systems that differentiate + between binary and text files, \code{'b'} appended to the mode opens + the file in binary mode. If the file cannot be opened, \code{IOError} + is raised. +\end{funcdesc} + +\begin{funcdesc}{ord}{c} + Return the \ASCII{} value of a string of one character. E.g., + \code{ord('a')} returns the integer \code{97}. This is the inverse of + \code{chr()}. +\end{funcdesc} + +\begin{funcdesc}{pow}{x\, y} + Return \var{x} to the power \var{y}. The arguments must have + numeric types. With mixed operand types, the rules for binary + arithmetic operators apply. The effective operand type is also the + type of the result; if the result is not expressible in this type, the + function raises an exception; e.g., \code{pow(2, -1)} is not allowed. +\end{funcdesc} + +\begin{funcdesc}{range}{start\, end\, step} + This is a versatile function to create lists containing arithmetic + progressions. It is most often used in \code{for} loops. The + arguments must be plain integers. If the \var{step} argument is + omitted, it defaults to \code{1}. If the \var{start} argument is + omitted, it defaults to \code{0}. The full form returns a list of + plain integers \code{[\var{start}, \var{start} + \var{step}, + \var{start} + 2 * \var{step}, \ldots]}. If \var{step} is positive, + the last element is the largest \code{\var{start} + \var{i} * + \var{step}} less than \var{end}; if \var{step} is negative, the last + element is the largest \code{\var{start} + \var{i} * \var{step}} + greater than \var{end}. \var{step} must not be zero. Example: + +\bcode\begin{verbatim} +>>> range(10) +[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] +>>> range(1, 11) +[1, 2, 3, 4, 5, 6, 7, 8, 9, 10] +>>> range(0, 30, 5) +[0, 5, 10, 15, 20, 25] +>>> range(0, 10, 3) +[0, 3, 6, 9] +>>> range(0, -10, -1) +[0, -1, -2, -3, -4, -5, -6, -7, -8, -9] +>>> range(0) +[] +>>> range(1, 0) +[] +>>> +\end{verbatim}\ecode +\end{funcdesc} + +\begin{funcdesc}{raw_input}{prompt} + The string argument is optional; if present, it is written to + standard + output without a trailing newline. The function then reads a line + from input, converts it to a string (stripping a trailing newline), + and returns that. When \EOF{} is read, \code{EOFError} is raised. + Example: + +\bcode\begin{verbatim} +>>> s = raw_input('--> ') +--> Monty Python's Flying Circus +>>> s +'Monty Python\'s Flying Circus' +>>> +\end{verbatim}\ecode +\end{funcdesc} + +\begin{funcdesc}{reduce}{function\, list\, initializer} +Apply the binary \var{function} to the items of \var{list} so as to +reduce the list to a single value. E.g., +\code{reduce(lambda x, y: x*y, \var{list}, 1)} returns the product of +the elements of \var{list}. The optional \var{initializer} can be +thought of as being prepended to \var{list} so as to allow reduction +of an empty \var{list}. The \var{list} arguments may be any kind of +sequence. +\end{funcdesc} + +\begin{funcdesc}{reload}{module} + Re-parse and re-initialize an already imported \var{module}. The + argument must be a module object, so it must have been successfully + imported before. This is useful if you have edited the module source + file using an external editor and want to try out the new version + without leaving the Python interpreter. Note that if a module is + syntactically correct but its initialization fails, the first + \code{import} statement for it does not import the name, but does + create a (partially initialized) module object; to reload the module + you must first \code{import} it again (this will just make the + partially initialized module object available) before you can + \code{reload()} it. +\end{funcdesc} + +\begin{funcdesc}{repr}{object} +Return a string containing a printable representation of an object. +This is the same value yielded by conversions (reverse quotes). +It is sometimes useful to be able to access this operation as an +ordinary function. For many types, this function makes an attempt +to return a string that would yield an object with the same value +when passed to \code{eval()}. +\end{funcdesc} + +\begin{funcdesc}{round}{x\, n} + Return the floating point value \var{x} rounded to \var{n} digits + after the decimal point. If \var{n} is omitted, it defaults to zero. + The result is a floating point number. Values are rounded to the + closest multiple of 10 to the power minus \var{n}; if two multiples + are equally close, rounding is done away from 0 (so e.g. + \code{round(0.5)} is \code{1.0} and \code{round(-0.5)} is \code{-1.0}). +\end{funcdesc} + +\begin{funcdesc}{setattr}{object\, name\, value} + This is the counterpart of \code{getattr}. The arguments are an + object, a string and an arbitrary value. The string must be the name + of one of the object's attributes. The function assigns the value to + the attribute, provided the object allows it. For example, + \code{setattr(\var{x}, '\var{foobar}', 123)} is equivalent to + \code{\var{x}.\var{foobar} = 123}. +\end{funcdesc} + +\begin{funcdesc}{str}{object} +Return a string containing a nicely printable representation of an +object. For strings, this returns the string itself. The difference +with \code{repr(\var{object}} is that \code{str(\var{object}} does not +always attempt to return a string that is acceptable to \code{eval()}; +its goal is to return a printable string. +\end{funcdesc} + +\begin{funcdesc}{type}{object} +% XXXJH xref to buil-in objects here? + Return the type of an \var{object}. The return value is a type + object. There is not much you can do with type objects except compare + them to other type objects; e.g., the following checks if a variable + is a string: + +\bcode\begin{verbatim} +>>> if type(x) == type(''): print 'It is a string' +\end{verbatim}\ecode +\end{funcdesc} |