How to find "in" in the documentation

Albert Hopkins marduk at letterboxes.org
Fri Mar 13 22:26:00 CET 2009


On Fri, 2009-03-13 at 21:01 +0000, tinnews at isbd.co.uk wrote:
> I've had this trouble before, how do I find the details of how "in"
> works in the documentation.  E.g. the details of:-
> 
>     if string in bigstring:
> 
> It gets a mention in the "if" section but not a lot.
> 

>From http://docs.python.org/reference/expressions.html#in

        The operators in and not in test for collection membership. x in
        s evaluates to true if x is a member of the collection s, and
        false otherwise. x not in s returns the negation of x in s. The
        collection membership test has traditionally been bound to
        sequences; an object is a member of a collection if the
        collection is a sequence and contains an element equal to that
        object. However, it make sense for many other object types to
        support membership tests without being a sequence. In
        particular, dictionaries (for keys) and sets support membership
        testing.
        
        For the list and tuple types, x in y is true if and only if
        there exists an index i such that x == y[i] is true.
        
        For the Unicode and string types, x in y is true if and only if
        x is a substring of y. An equivalent test is y.find(x) != -1.
        Note, x and y need not be the same type; consequently, u'ab' in
        'abc' will return True. Empty strings are always considered to
        be a substring of any other string, so "" in "abc" will return
        True.
        
        Changed in version 2.3: Previously, x was required to be a
        string of length 1.
        
        For user-defined classes which define the __contains__() method,
        x in y is true if and only if y.__contains__(x) is true.
        
        For user-defined classes which do not define __contains__() and
        do define __getitem__(), x in y is true if and only if there is
        a non-negative integer index i such that x == y[i], and all
        lower integer indices do not raise IndexError exception. (If any
        other exception is raised, it is as if in raised that
        exception).





More information about the Python-list mailing list