Python compiled pattern match with flags, cp.search to match at beginning of line

Question

I have this, which gives no match, why ?:

>>> p = r'abc'
>>> cp = re.compile(p, re.IGNORECASE)
>>> m = cp.search('ABC', re.IGNORECASE)
>>> m # NO MATCH # 1

But, this gives a match, why ?

>>> m = cp.search('  ABC', re.IGNORECASE) # introduced spaces, ABC no longer at the beginning 
>>> m # MATCH # 2
<_sre.SRE_Match object at 0x1082b5ac0>

To get a match in #1 all I have to do is drop re.IGNORECASE, why so ?

>>> m = cp.search('ABC')
>>> m
<_sre.SRE_Match object at 0x10827e308>

Dewald Abrie · Accepted Answer · 2017-08-28 03:22:19Z

1

If (in the interpreter) you print out the help on cp.search:

help(cp.search)

you will see:

Help on built-in function search:
search(string=None, pos=0, endpos=9223372036854775807, *, pattern=None) method of _sre.SRE_Pattern instance
    Scan through string looking for a match, and return a corresponding match object instance.

    Return None if no position in the string matches.

Notice that this function does not take any flags, but what you were actually passing your flag to the 'pos' argument, which was why you got an unexpected result.

answered Aug 28, 2017 at 3:22

Dewald Abrie

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4 Comments

Ankur Agarwal Over a year ago

How'd you get pos=0, endpos=9223372036854775807 in your method help ? I don't see that. But what you said makes total sense. Thanks

Dewald Abrie Over a year ago

@abc No idea, maybe we're running different versions of Python.

Ankur Agarwal Over a year ago

$ python --version Python 2.7.10

Dewald Abrie Over a year ago

@abc I was using Python 3.6

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