CODEWITHSUNDEEP
pythonregex
D. Horton
D. Horton

Reputation: 29

How to re.compile a variable in Python?

I am a beginner. This seems so simple, but I have spent hours searching and trying different things with no luck. I want to express the string I am compiling as a variable.

So this works:

p = re.compile("['4c']")

for m in p.finditer('234567891JQKA'):
    q = str(m.start() + 2)

While this doesn't:

card = ['4c']
p = re.compile(card)

for m in p.finditer('234567891JQKA'):
    q = str(m.start() + 2)

In my program card is constantly changing. How do I do this?

The error I get is:

File "C:\Python34\lib\re.py", line 223, in compile
return _compile(pattern, flags)
File "C:\Python34\lib\re.py", line 282, in _compile
p, loc = _cache[type(pattern), pattern, flags]
TypeError: unhashable type: 'list'

Upvotes: 1

Views: 2884

Answers (2)

J0e3gan
J0e3gan

Reputation: 8938

The problem in your second example is that you assign ['4c'] (a list) to card rather than "['4c']" (the string that works in your first example). re.compile expects a string pattern.

Adjust as follows, and your second example will work like your first example:

import re # added for clarity

card = "['4c']"
#      ^      ^
p = re.compile(card)

# or

card = ['4c']
p = re.compile(str(card))  # str(card) == "['4c']"
#              ^^^^    ^

for m in p.finditer('234567891JQKA'):
    q = str(m.start() + 2)
    # added for clarity
    print m.start()  # prints 2
    print q          # prints 4

Having said this, the pattern "['4c']" seems suspect. At minimum, ' is redundant within the regex character set (bounded by the opening [ and the closing ]): make sure card is a string that specifies a sensible regex pattern for your needs.

Upvotes: 2

fronthem
fronthem

Reputation: 4139

There are at least two mistakes in your program

First, a strange Regex wildcard

You suppose to read at least a basic regex before you using it, you explicitly misunderstand it, here some useful cheat sheet and manual.

['4c'] (wrong! it stands for either one character ', 4 or c but there is duplicated ')

['4c] (right! it stands for either one character ', 4 or c),

[4c'] (right! it stands for either one character ', 4 or c),

[4c] (right! it stands for either one character 4 or c)

Second, Python list != Regex wildcard

['4c'] is a list which contains string '4c',

"['4c']" is a string which contain regular expression wildcard.

Finally, if you prefer to use the second form of your code, your code suppose to look like this

card = "['4c']" # not clear here what you want to do
p = re.compile(card)

for m in p.finditer('234567891JQKA'):
    q = str(m.start() + 2)

Upvotes: 1

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