[ python-Feature Requests-1190701 ] Add 'before' and 'after' methods to Strings

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Feature Requests item #1190701, was opened at 2005-04-26 20:35
Message generated for change (Comment added) made by cxdunn
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Christopher Dunn (cxdunn)
Assigned to: Nobody/Anonymous (nobody)
Summary: Add 'before' and 'after' methods to Strings

Initial Comment:
GNU String used to have two very useful methods,
'before' and 'after'. These are so useful I keep them
defined in an __init__.py file. (Unfortunately, I do
not know how to make them methods, instead of global
functions.)

Usage:

>>> "root.sub".before(".")
'root'
>>> "root.sub1.sub2".after("root.sub1")
'.sub2'

They work like s.split(word)[0], and s.split(word)[-1],
but they are so intuitive they ought to be part of the
interface.

I'm not sure whether they should raise exceptions on
failure, or simply return the whole string.

-cxdunn

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>Comment By: Christopher Dunn (cxdunn)
Date: 2005-04-28 01:40

Message:
Logged In: YES 
user_id=1267419

Your examples prove my point:

>>> s = "root.sub"
>>> t = "fubar"
>>> s[:s.find(t)]
'root.su'

>>> s = "root.sub1.sub2"
>>> t = "fubar"
>>> s[s.find(sep)+len(sep):]
'.sub1.sub2'

string.find() is the wrong way.
I can live with string.split():
>>> "root.sub1.sub2"
>>> t = '.'
>>> s.split(t)[0]
'root'
>>> s.split(t)[-1]
'sub2'
>>> t = "fubar"
>>> s.split(t)[0]
'root.sub1.sub2'
>>> s.split(t)[-1]
'root.sub1.sub2'

This is not terrible, but the desired behavior is really
more like strip/rstrip::

def before( s, first ):
    """Find first inside string s and return everything
before that.
    >>> before('xyz.pdq.abc', '.')
    'xyz'
    >>> before('xyz.pdq.abc', 'fubar')
    'xyz.pdq.abc'
    """
    return s.split(first)[0]
def after( s, first ):
    """Find first inside string s and return everything
after that.
    >>> after('xyz.pdq.abc', '.')
    'pdq.abc'
    >>> after('xyz.pdq', 'xyz.')
    'pdq'
    >>> after('xyz.pdq.abc', 'fubar')
    ''
    """
    return first.join(s.split(first)[1:])
def rbefore( s, last ):
    """Find last inside string s, from the right,
    and return everything before that.
    >>> rbefore('xyz.pdq.abc', '.')
    'xyz.pdq'
    >>> rbefore('xyz.pdq.abc', 'fubar')
    ''
    """
    return last.join(s.split(last)[:-1])
def rafter( s, last ):
    """Find last inside string s, from the right
    and return everything after that.
    >>> rafter('xyz.pdq.abc', '.')
    'abc'
    >>> rafter('xyz.pdq.abc', 'fubar')
    'xyz.pdq.abc'
    """
    return s.split(last)[-1]

It's a question of elegance. These are very useful,
infuitive functions, and I cannot add them to string myself.
And as you've seen, it's easy to create bugs when you try to
do this on the fly.

Reconsider? If not, I'll just post it in the Cookbook, to
point out the dangers of relying on string.find.

----------------------------------------------------------------------

Comment By: Raymond Hettinger (rhettinger)
Date: 2005-04-28 00:15

Message:
Logged In: YES 
user_id=80475

I'm -1 on expanding the string API for something so easily
coded with existing primitives:

>>> s = "root.sub"
>>> t = "."
>>> s[:s.find(t)]
'root'

>>> s = "root.sub1.sub2"
>>> t = "root.sub1"
>>> s[s.find(sep)+len(sep):]
'sub1.sub2'

----------------------------------------------------------------------

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