diff options
Diffstat (limited to 'Doc/lib/libfuncs.tex')
| -rw-r--r-- | Doc/lib/libfuncs.tex | 107 |
1 files changed, 72 insertions, 35 deletions
diff --git a/Doc/lib/libfuncs.tex b/Doc/lib/libfuncs.tex index 0eb6857..4778c7d 100644 --- a/Doc/lib/libfuncs.tex +++ b/Doc/lib/libfuncs.tex @@ -92,8 +92,8 @@ exactly one argument.) \var{expression} argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the \var{globals} and \var{locals} dictionaries as global and local name - space. If the \var{globals} dictionary is omitted it defaults to - the \var{locals} dictionary. If both dictionaries are omitted, the + space. If the \var{locals} dictionary is omitted it defaults to + the \var{globals} dictionary. If both dictionaries are omitted, the expression is executed in the environment where \code{eval} is called. The return value is the result of the evaluated expression. Syntax errors are reported as exceptions. Example: @@ -119,20 +119,21 @@ exactly one argument.) \end{funcdesc} \begin{funcdesc}{execfile}{file\optional{\, globals\optional{\, locals}}} - This function is similar to the \code{eval()} function or the + This function is similar to the \code{exec} statement, but parses a file instead of a string. It is different from the \code{import} statement in that it does not use the module administration --- it reads the file unconditionally and - does not create a new module. + does not create a new module.\footnote{It is used relatively rarely + so does not warrant being made into a statement.} The arguments are a file name and two optional dictionaries. The file is parsed and evaluated as a sequence of Python statements (similarly to a module) using the \var{globals} and \var{locals} - dictionaries as global and local name space. If the \var{globals} - dictionary is omitted it defaults to the \var{locals} dictionary. + dictionaries as global and local name space. If the \var{locals} + dictionary is omitted it defaults to the \var{globals} dictionary. If both dictionaries are omitted, the expression is executed in the - environment where \code{execfile} is called. The return value is - None. + environment where \code{execfile()} is called. The return value is + \code{None}. \end{funcdesc} \begin{funcdesc}{filter}{function\, list} @@ -173,8 +174,8 @@ removed. \end{funcdesc} \begin{funcdesc}{hex}{x} - Convert a number to a hexadecimal string. The result is a valid - Python expression. + Convert an integer number (of any size) to a hexadecimal string. + The result is a valid Python expression. \end{funcdesc} \begin{funcdesc}{id}{object} @@ -194,7 +195,9 @@ removed. \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. + long integer or a floating point number. Conversion of floating + point numbers to integers is defined by the C semantics; normally + the conversion truncates towards zero. \end{funcdesc} \begin{funcdesc}{len}{s} @@ -231,8 +234,8 @@ any kind of sequence; the result is always a list. \end{funcdesc} \begin{funcdesc}{oct}{x} - Convert a number to an octal string. The result is a valid Python - expression. + Convert an integer number (of any size) to an octal string. The + result is a valid Python expression. \end{funcdesc} \begin{funcdesc}{open}{filename\optional{\, mode\optional{\, bufsize}}} @@ -290,7 +293,8 @@ there's no reliable way to determine whether this is the case.} 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: + greater than \var{end}. \var{step} must not be zero (or else an + exception is raised). Example: \bcode\begin{verbatim} >>> range(10) @@ -321,7 +325,7 @@ there's no reliable way to determine whether this is the case.} >>> s = raw_input('--> ') --> Monty Python's Flying Circus >>> s -'Monty Python\'s Flying Circus' +"Monty Python's Flying Circus" >>> \end{verbatim}\ecode \end{funcdesc} @@ -337,17 +341,48 @@ 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. +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. The return value is the +module object (i.e.\ the same as the \var{module} argument). + +There are a number of caveats: + +If a module is syntactically correct but its initialization fails, the +first \code{import} statement for it does not bind its name locally, +but does store a (partially initialized) module object in +\code{sys.modules}. To reload the module you must first +\code{import} it again (this will bind the name to the partially +initialized module object) before you can \code{reload()} it. + +When a module is reloaded, its dictionary (containing the module's +global variables) is retained. Redefinitions of names will override +the old definitions, so this is generally not a problem. If the new +version of a module does not define a name that was defined by the old +version, the old definition remains. This feature can be used to the +module's advantage if it maintains a global table or cache of objects +--- with a \code{try} statement it can test for the table's presence +and skip its initialization if desired. + +It is legal though generally not very useful to reload built-in or +dynamically loaded modules, except for \code{sys}, \code{__main__} and +\code{__builtin__}. In certain cases, however, extension modules are +not designed to be initialized more than once, and may fail in +arbitrary ways when reloaded. + +If a module imports objects from another module using \code{from} +{\ldots} \code{import} {\ldots}, calling \code{reload()} for the other +module does not redefine the objects imported from it --- one way +around this is to re-execute the \code{from} statement, another is to +use \code{import} and qualified names (\var{module}.\var{name}) +instead. + +If a module instantiates instances of a class, reloading the module +that defines the class does not affect the method definitions of the +instances --- they continue to use the old class definition. The same +is true for derived classes. \end{funcdesc} \begin{funcdesc}{repr}{object} @@ -385,23 +420,25 @@ always attempt to return a string that is acceptable to \code{eval()}; its goal is to return a printable string. \end{funcdesc} -\begin{funcdesc}{tuple}{object} +\begin{funcdesc}{tuple}{sequence} Return a tuple whose items are the same and in the same order as -\var{object}'s items. If \var{object} is alread a tuple, it +\var{sequence}'s items. If \var{sequence} is alread a tuple, it is returned unchanged. For instance, \code{tuple('abc')} returns returns \code{('a', 'b', 'c')} and \code{tuple([1, 2, 3])} returns \code{(1, 2, 3)}. \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: +Return the type of an \var{object}. The return value is a type +object. The standard module \code{types} defines names for all +built-in types. +\stmodindex{types} +\obindex{type} +For instance: \bcode\begin{verbatim} ->>> if type(x) == type(''): print 'It is a string' +>>> import types +>>> if type(x) == types.StringType: print "It's a string" \end{verbatim}\ecode \end{funcdesc} @@ -424,7 +461,7 @@ which yields the same values as the corresponding list, without actually storing them all simultaneously. The advantage of \code{xrange()} over \code{range()} is minimal (since \code{xrange()} still has to create the values when asked for them) except when a very -large range is used on a memory-starved machine (e.g. DOS) or when all +large range is used on a memory-starved machine (e.g. MS-DOS) or when all of the range's elements are never used (e.g. when the loop is usually terminated with \code{break}). \end{funcdesc} |