I tried running the following code:
lin = ',11'
pat = ',([11|01])$'
re.search(pat, lin)
since pat has ',11' and lin also has ',11' I should get an object returned by re.search
But in this case, it is returning None.
Can anybody please help me out? I'm pretty confused over it.
You are using a character class: [...]. These act as sets; any of the characters you name in them will match. Your character class will match any 1, | or 0 character, the 3 unique characters you named in the class. You didn't specify a multiplier after the [...] character class, so it'll match just one character:
>>> re.match(',([11|01])$', ',1')
<_sre.SRE_Match object at 0x1106d1648>
>>> re.match(',([11|01])$', ',0')
<_sre.SRE_Match object at 0x1106d16c0>
>>> re.match(',([11|01])$', ',|')
<_sre.SRE_Match object at 0x1106d1648>
Remove the class if you want to match exact characters:
pat = ',(11|01)$'
which matches either the literal characters 11 or 01:
>>> re.match(',(11|01)$', ',11')
<_sre.SRE_Match object at 0x1106d16c0>
>>> re.match(',(11|01)$', ',01')
<_sre.SRE_Match object at 0x1106d1648>
or, if you still want to use a character class:
pat = ',([01]1)$'
Now the parenthesis are no longer required to group the | or operator, so you can drop those to simplify things down to:
pat = ',[01]1$'
Demo:
>>> re.match(',[01]1$', ',01')
<_sre.SRE_Match object at 0x1106bc5e0>
>>> re.match(',[01]1$', ',11')
<_sre.SRE_Match object at 0x1106bc648>
>>> re.match(',[01]1$', ',00') is None
True
>>> re.match(',[01]1$', ',10') is None
True
>>> re.match(',[01]1$', ',|') is None
True
Due to the [...] brackets, your regular expression matches one character, which may be 0, 1, or |.
I think you wanted more like ,(11|01)$.
[11|01] is not 11 or 01, it is actually 1 or | or 0.
Try using this:
,[10]1$
That would be a comma, then [1 or 0], then 1, then an anchor to the end of string.
You could also just use this:
,((11)|(01))$
