Geek asks and answers

Too many indentation when checking a string with many regular expressions sequentially in python

I get a deep indent when I write code as shown below

match = re.search(some_regex_1, s)
if match:
    # do something with match data
else:
    match = re.search(some_regex_2, s)
    if match:
        # do something with match data
    else:
        match = re.search(soem_regex_3, s)
        if match:
            # do something with match data
        else:
            # ...
            # and so on

I tried to rewrite as:

if match = re.search(some_regex_1, s):
    # ...
elif match = re.search(some_regex_2, s):
    # ...
elif ....
    # ...
...

but Python does not allow the use of this syntax. What to do to avoid deep deepening in this case?

+3
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4 answers
regexes = (regex1, regex2, regex3)
for regex in regexes:
    match = re.search(regex, s)
    if match:
        #do stuff
        break

Alternative (more advanced):

def process1(match_obj):
    #handle match 1

def process2(match_obj):
    #handle match 2

def process3(match_obj):
    #handle match 3
.
.
.
handler_map = ((regex1, process1), (regex2, process2), (regex3, process3))
for regex, handler in handler_map:
    match = re.search(regex, s)
    if match:
        result = handler(match)
        break
else:
    #else condition if no regex matches
+6
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If you can use finditer()instead search()(most of the time you can), you can combine all your regular expressions into one and use the names of symbolic groups. Here is an example:

import re

regex = """
   (?P<number> \d+ ) |
   (?P<word> \w+ ) |
   (?P<punctuation> \. | \! | \? | \, | \; | \: ) |
   (?P<whitespace> \s+ ) |
   (?P<eof> $ ) |
   (?P<error> \S )
"""

scan = re.compile(pattern=regex, flags=re.VERBOSE).finditer

for match in scan('Hi, my name is Joe. I am 1 programmer.'):
    token_type = match.lastgroup
    if token_type == 'number':
        print 'found number "%s"' % match.group()
    elif token_type == 'word':
        print 'found word "%s"' % match.group()
    elif token_type == 'punctuation':
        print 'found punctuation character "%s"' % match.group()
    elif token_type == 'whitespace':
        print 'found whitespace'
    elif token_type == 'eof':
        print 'done parsing'
        break
    else:
        raise ValueError('String kaputt!')
+2
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if re.search(some_regex_1, s) is not None:
    # ...
elif re.search(some_regex_2, s) is not None:
    # ...
elif ....
    # ...
...

search() None, , if .

0

I found the corresponding answer in another thread that uses a class to save data to emulate an assignment idiom in state in C

fooobar.com/questions/126062 / ...

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