diff options
Diffstat (limited to 'Doc/lib/libcollections.tex')
-rw-r--r-- | Doc/lib/libcollections.tex | 66 |
1 files changed, 58 insertions, 8 deletions
diff --git a/Doc/lib/libcollections.tex b/Doc/lib/libcollections.tex index 5a07a2d..33ace7d 100644 --- a/Doc/lib/libcollections.tex +++ b/Doc/lib/libcollections.tex @@ -9,14 +9,16 @@ This module implements high-performance container datatypes. Currently, -there are two datatypes, deque and defaultdict. +there are two datatypes, deque and defaultdict, and one datatype factory +function, \function{NamedTuple}. Future additions may include balanced trees and ordered dictionaries. \versionchanged[Added defaultdict]{2.5} +\versionchanged[Added NamedTuple]{2.6} \subsection{\class{deque} objects \label{deque-objects}} -\begin{funcdesc}{deque}{\optional{iterable}} - Returns a new deque objected initialized left-to-right (using +\begin{classdesc}{deque}{\optional{iterable}} + Returns a new deque object initialized left-to-right (using \method{append()}) with data from \var{iterable}. If \var{iterable} is not specified, the new deque is empty. @@ -30,7 +32,7 @@ Future additions may include balanced trees and ordered dictionaries. for \samp{pop(0)} and \samp{insert(0, v)} operations which change both the size and position of the underlying data representation. \versionadded{2.4} -\end{funcdesc} +\end{classdesc} Deque objects support the following methods: @@ -219,7 +221,7 @@ def maketree(iterable): \subsection{\class{defaultdict} objects \label{defaultdict-objects}} -\begin{funcdesc}{defaultdict}{\optional{default_factory\optional{, ...}}} +\begin{classdesc}{defaultdict}{\optional{default_factory\optional{, ...}}} Returns a new dictionary-like object. \class{defaultdict} is a subclass of the builtin \class{dict} class. It overrides one method and adds one writable instance variable. The remaining functionality is the same as @@ -231,7 +233,7 @@ def maketree(iterable): passed to the \class{dict} constructor, including keyword arguments. \versionadded{2.5} -\end{funcdesc} +\end{classdesc} \class{defaultdict} objects support the following method in addition to the standard \class{dict} operations: @@ -254,11 +256,11 @@ the standard \class{dict} operations: \class{defaultdict} objects support the following instance variable: -\begin{datadesc}{default_factory} +\begin{memberdesc}{default_factory} This attribute is used by the \method{__missing__} method; it is initialized from the first argument to the constructor, if present, or to \code{None}, if absent. -\end{datadesc} +\end{memberdesc} \subsubsection{\class{defaultdict} Examples \label{defaultdict-examples}} @@ -339,3 +341,51 @@ Setting the \member{default_factory} to \class{set} makes the >>> d.items() [('blue', set([2, 4])), ('red', set([1, 3]))] \end{verbatim} + + + +\subsection{\function{NamedTuple} datatype factory function \label{named-tuple-factory}} + +\begin{funcdesc}{NamedTuple}{typename, fieldnames} + Returns a new tuple subclass named \var{typename}. The new subclass is used + to create tuple-like objects that have fields accessable by attribute + lookup as well as being indexable and iterable. Instances of the subclass + also have a helpful docstring (with typename and fieldnames) and a helpful + \method{__repr__()} method which lists the tuple contents in a \code{name=value} + format. + \versionadded{2.6} + + The \var{fieldnames} are specified in a single string and are separated by spaces. + Any valid Python identifier may be used for a field name. + + Example: + \begin{verbatim} +>>> Point = NamedTuple('Point', 'x y') +>>> Point.__doc__ # docstring for the new datatype +'Point(x, y)' +>>> p = Point(11, y=22) # instantiate with positional or keyword arguments +>>> p[0] + p[1] # works just like the tuple (11, 22) +33 +>>> x, y = p # unpacks just like a tuple +>>> x, y +(11, 22) +>>> p.x + p.y # fields also accessable by name +33 +>>> p # readable __repr__ with name=value style +Point(x=11, y=22) +\end{verbatim} + + The use cases are the same as those for tuples. The named factories + assign meaning to each tuple position and allow for more readable, + self-documenting code. Named tuples can also be used to assign field names + to tuples + returned by the \module{csv} or \module{sqlite3} modules. For example: + + \begin{verbatim} +import csv +EmployeeRecord = NamedTuple('EmployeeRecord', 'name age title department paygrade') +for tup in csv.reader(open("employees.csv", "rb")): + print EmployeeRecord(*tup) +\end{verbatim} + +\end{funcdesc} |