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Diffstat (limited to 'Doc/tut/tut.tex')
| -rw-r--r-- | Doc/tut/tut.tex | 104 |
1 files changed, 48 insertions, 56 deletions
diff --git a/Doc/tut/tut.tex b/Doc/tut/tut.tex index 6927afe..14261aa 100644 --- a/Doc/tut/tut.tex +++ b/Doc/tut/tut.tex @@ -238,7 +238,7 @@ not consumed by the Python interpreter's option processing but left in When commands are read from a tty, the interpreter is said to be in \emph{interactive mode}. In this mode it prompts for the next command with the \emph{primary prompt}, usually three greater-than signs -(\samp{>>>~}); for continuation lines it prompts with the +(\samp{>\code{>}>~}); for continuation lines it prompts with the \emph{secondary prompt}, by default three dots (\samp{...~}). The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt, e.g.: @@ -340,7 +340,7 @@ if filename and os.path.isfile(filename): \chapter{An Informal Introduction to Python \label{informal}} In the following examples, input and output are distinguished by the -presence or absence of prompts (\samp{>>>~} and \samp{...~}): to repeat +presence or absence of prompts (\samp{>\code{>}>~} and \samp{...~}): to repeat the example, you must type everything after the prompt, when the prompt appears; lines that do not begin with a prompt are output from the interpreter. % @@ -372,7 +372,7 @@ STRING = "# This is not a comment." \section{Using Python as a Calculator \label{calculator}} Let's try some simple Python commands. Start the interpreter and wait -for the primary prompt, \samp{>>> }. (It shouldn't take long.) +for the primary prompt, \samp{>\code{>}>~}. (It shouldn't take long.) \subsection{Numbers \label{numbers}} @@ -420,7 +420,7 @@ A value can be assigned to several variables simultaneously: >>> z 0 \end{verbatim} -% + There is full support for floating point; operators with mixed type operands convert the integer operand to floating point: @@ -430,7 +430,7 @@ operands convert the integer operand to floating point: >>> 7.0 / 2 3.5 \end{verbatim} -% + Complex numbers are also supported; imaginary numbers are written with a suffix of \samp{j} or \samp{J}. Complex numbers with a nonzero real component are written as \samp{(\var{real}+\var{imag}j)}, or can @@ -448,7 +448,7 @@ be created with the \samp{complex(\var{real}, \var{imag})} function. >>> (1+2j)/(1+1j) (1.5+0.5j) \end{verbatim} -% + Complex numbers are always represented as two floating point numbers, the real and imaginary part. To extract these parts from a complex number \var{z}, use \code{\var{z}.real} and \code{\var{z}.imag}. @@ -460,7 +460,7 @@ number \var{z}, use \code{\var{z}.real} and \code{\var{z}.imag}. >>> a.imag 0.5 \end{verbatim} -% + The conversion functions to floating point and integer (\function{float()}, \function{int()} and \function{long()}) don't work for complex numbers --- there is no one correct way to convert a @@ -478,7 +478,7 @@ TypeError: can't convert complex to float; use e.g. abs(z) >>> abs(a) 1.58113883008 \end{verbatim} -% + In interactive mode, the last printed expression is assigned to the variable \code{_}. This means that when you are using Python as a desk calculator, it is somewhat easier to continue calculations, for @@ -749,9 +749,9 @@ in every script used in modern and ancient texts. Previously, there were only 256 possible ordinals for script characters and texts were typically bound to a code page which mapped the ordinals to script characters. This lead to very much confusion especially with respect -to internalization (usually written as \samp{i18n} --- \character{i} + -18 characters + \character{n}) of software. Unicode solves these -problems by defining one code page for all scripts. +to internationalization (usually written as \samp{i18n} --- +\character{i} + 18 characters + \character{n}) of software. Unicode +solves these problems by defining one code page for all scripts. Creating Unicode strings in Python is just as simple as creating normal strings: @@ -1167,6 +1167,7 @@ which searches for prime numbers: 9 equals 3 * 3 \end{verbatim} + \section{\keyword{pass} Statements \label{pass}} The \keyword{pass} statement does nothing. @@ -1180,6 +1181,7 @@ For example: ... \end{verbatim} + \section{Defining Functions \label{functions}} We can create a function that writes the Fibonacci series to an @@ -1277,7 +1279,7 @@ the Fibonacci series, instead of printing it: >>> f100 # write the result [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89] \end{verbatim} -% + This example, as usual, demonstrates some new Python features: \begin{itemize} @@ -1467,6 +1469,7 @@ shopkeeper : Michael Palin sketch : Cheese Shop Sketch \end{verbatim} + \subsection{Arbitrary Argument Lists \label{arbitraryArgs}} Finally, the least frequently used option is to specify that a @@ -1753,6 +1756,7 @@ item, then to the result and the next item, and so on. For example, 0 \end{verbatim} + \subsection{List Comprehensions} List comprehensions provide a concise way to create lists without resorting @@ -1795,6 +1799,7 @@ SyntaxError: invalid syntax [6, 5, -7, 8, 7, -5, 10, 9, -3] \end{verbatim} + \section{The \keyword{del} statement \label{del}} There is a way to remove an item from a list given its index instead @@ -1823,6 +1828,7 @@ Referencing the name \code{a} hereafter is an error (at least until another value is assigned to it). We'll find other uses for \keyword{del} later. + \section{Tuples and Sequences \label{tuples}} We saw that lists and strings have many common properties, e.g., @@ -1855,7 +1861,8 @@ Tuples have many uses, e.g., (x, y) coordinate pairs, employee records from a database, etc. Tuples, like strings, are immutable: it is not possible to assign to the individual items of a tuple (you can simulate much of the same effect with slicing and concatenation, -though). +though). It is also possible to create tuples which contain mutable +objects, such as lists. A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty @@ -1884,24 +1891,17 @@ is also possible, e.g.: >>> x, y, z = t \end{verbatim} -This is called, appropriately enough, \emph{tuple unpacking}. Tuple -unpacking requires that the list of variables on the left have the same -number of elements as the length of the tuple. Note that multiple -assignment is really just a combination of tuple packing and tuple -unpacking! +This is called, appropriately enough, \emph{sequence unpacking}. +Sequence unpacking requires that the list of variables on the left +have the same number of elements as the length of the sequence. Note +that multiple assignment is really just a combination of tuple packing +and sequence unpacking! -% XXX This is no longer necessary! -Occasionally, the corresponding operation on lists is useful: \emph{list -unpacking}. This is supported by enclosing the list of variables in -square brackets: - -\begin{verbatim} ->>> a = ['spam', 'eggs', 100, 1234] ->>> [a1, a2, a3, a4] = a -\end{verbatim} +There is a small bit of asymmetry here: packing multiple values +always creates a tuple, and unpacking works for any sequence. % XXX Add a bit on the difference between tuples and lists. -% XXX Also explain that a tuple can *contain* a mutable object! + \section{Dictionaries \label{dictionaries}} @@ -1911,11 +1911,14 @@ memories'' or ``associative arrays''. Unlike sequences, which are indexed by a range of numbers, dictionaries are indexed by \emph{keys}, which can be any immutable type; strings and numbers can always be keys. Tuples can be used as keys if they contain only strings, -numbers, or tuples. You can't use lists as keys, since lists can be -modified in place using their \code{append()} method. +numbers, or tuples; if a tuple contains any mutable object either +directly or indirectly, it cannot be used as a key. You can't use +lists as keys, since lists can be modified in place using their +\method{append()} and \method{extend()} methods, as well as slice and +indexed assignments. It is best to think of a dictionary as an unordered set of -\emph{key:value} pairs, with the requirement that the keys are unique +\emph{key: value} pairs, with the requirement that the keys are unique (within one dictionary). A pair of braces creates an empty dictionary: \code{\{\}}. Placing a comma-separated list of key:value pairs within the @@ -2001,6 +2004,7 @@ C programmers may grumble about this, but it avoids a common class of problems encountered in C programs: typing \code{=} in an expression when \code{==} was intended. + \section{Comparing Sequences and Other Types \label{comparing}} Sequence objects may be compared to other objects with the same @@ -2102,7 +2106,7 @@ Using the module name you can access the functions: >>> fibo.__name__ 'fibo' \end{verbatim} -% + If you intend to use a function often you can assign it to a local name: \begin{verbatim} @@ -2164,9 +2168,8 @@ There is even a variant to import all names that a module defines: This imports all names except those beginning with an underscore (\code{_}). -\subsection{The Module Search Path \label{searchPath}} -% XXX Need to document that a lone .pyc/.pyo is acceptable too! +\subsection{The Module Search Path \label{searchPath}} \indexiii{module}{search}{path} When a module named \module{spam} is imported, the interpreter searches @@ -2238,13 +2241,14 @@ When a script is run by giving its name on the command line, the bytecode for the script is never written to a \file{.pyc} or \file{.pyo} file. Thus, the startup time of a script may be reduced by moving most of its code to a module and having a small bootstrap -script that imports that module. +script that imports that module. It is also possible to name a +\file{.pyc} or \file{.pyo} file directly on the command line. \item It is possible to have a file called \file{spam.pyc} (or -\file{spam.pyo} when \programopt{-O} is used) without a module -\file{spam.py} in the same module. This can be used to distribute -a library of Python code in a form that is moderately hard to reverse +\file{spam.pyo} when \programopt{-O} is used) without a file +\file{spam.py} for the same module. This can be used to distribute a +library of Python code in a form that is moderately hard to reverse engineer. \item @@ -2343,6 +2347,7 @@ standard module \module{__builtin__}\refbimodindex{__builtin__}: 'reduce', 'reload', 'repr', 'round', 'setattr', 'str', 'type', 'xrange'] \end{verbatim} + \section{Packages \label{packages}} Packages are a way of structuring Python's module namespace @@ -2392,6 +2397,7 @@ Sound/ Top-level package karaoke.py ... \end{verbatim} + The \file{__init__.py} files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as \samp{string}, from @@ -2406,17 +2412,20 @@ package, for example: \begin{verbatim} import Sound.Effects.echo \end{verbatim} + This loads the submodule \module{Sound.Effects.echo}. It must be referenced with its full name, e.g. \begin{verbatim} Sound.Effects.echo.echofilter(input, output, delay=0.7, atten=4) \end{verbatim} + An alternative way of importing the submodule is: \begin{verbatim} from Sound.Effects import echo \end{verbatim} + This also loads the submodule \module{echo}, and makes it available without its package prefix, so it can be used as follows: @@ -2500,7 +2509,6 @@ import Sound.Effects.surround from Sound.Effects import * \end{verbatim} - In this example, the echo and surround modules are imported in the current namespace because they are defined in the \module{Sound.Effects} package when the \code{from...import} statement @@ -2664,7 +2672,7 @@ minus signs: >>> string.zfill('3.14159265359', 5) '3.14159265359' \end{verbatim} -% + Using the \code{\%} operator looks like this: \begin{verbatim} @@ -3630,7 +3638,6 @@ class Bag: self.add(x) \end{verbatim} - Methods may reference global names in the same way as ordinary functions. The global scope associated with a method is the module containing the class definition. (The class itself is never used as a @@ -3790,20 +3797,6 @@ class VirtualAttributes: self.__vdict[name] = value \end{verbatim} -%\emph{Warning: this is an experimental feature.} To avoid all -%potential problems, refrain from using identifiers starting with -%double underscore except for predefined uses like \samp{__init__}. To -%use private names while maintaining future compatibility: refrain from -%using the same private name in classes related via subclassing; avoid -%explicit (manual) mangling/unmangling; and assume that at some point -%in the future, leading double underscore will revert to being just a -%naming convention. Discussion on extensive compile-time declarations -%are currently underway, and it is impossible to predict what solution -%will eventually be chosen for private names. Double leading -%underscore is still a candidate, of course --- just not the only one. -%It is placed in the distribution in the belief that it is useful, and -%so that widespread experience with its use can be gained. It will not -%be removed without providing a better solution and a migration path. \section{Odds and Ends \label{odds}} @@ -3823,7 +3816,6 @@ john.dept = 'computer lab' john.salary = 1000 \end{verbatim} - A piece of Python code that expects a particular abstract data type can often be passed a class that emulates the methods of that data type instead. For instance, if you have a function that formats some |