[Tutor] Re Module

[Steven D'Aprano]

On Thu, Dec 27, 2018 at 08:40:12PM +0530, Asad wrote:
> Hi All ,
> 
>           I trying find a solution for my script , I have two files :
> 
> file1 - I need a search a error say x if the error matches
> 
> Look for the same error x in other file 2
> 
> Here is the code :
> I have 10 different patterns therefore I used list comprehension and
> compiling the pattern so I loop over and find the exact pattern matching
> 
> re_comp1 = [re.compile(pattern) for pattern in str1]


You can move the IGNORECASE flag into the call to compile. Also, perhaps 
you can use better names instead of "str1" (one string?).

patterns = [re.compile(pattern, re.IGNORECASE) for pattern in string_patterns]
 
> for pat in re_comp1:
>     if pat.search(st,re.IGNORECASE):
>         x = pat.pattern
> print x                ===> here it gives the expected output it correct
> match
> print type(x)
> <type 'unicode'>

Be careful here: even though you have ten different patterns, only *one* 
will be stored in x. If three patterns match, x will only get the last 
of the three and the others will be ignored.

 
> if re.search('x', line, re.IGNORECASE) is not None:  ===> Gives a wrong match

That's because you are trying to match the literal string "x", so it 
will match anything with the letter "x":

box, text, ax, equinox, except, hexadecimal, fix, Kleenex, sixteen ...


> Instead if I use :
> 
> if re.search(x, line, re.IGNORECASE) is not None: then no match occurs
>       print line

Here you are trying to match the variable called x. That is a very bad 
name for a variable (what does "x" mean?) but it should work.

If no match occurs, it probably means that the value of x doesn't occur 
in the line you are looking at.

Try printing x and line and see if they are what you expect them to be:

print x
print line


-- 
Steve