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How to Validate Strings in Python with Regex


Let's say you need to validate strings in Python. Making decisions if a string is valid or not, is what we will be looking at today.

The Scenario

We have a string that will look like this: my-random-abc-string-2947104284738593726152637836291. The abc section will always be 3 random string characters and the integers, will always be 32 integer characters, the rest will always stay the same.

Using the re library, we will create our regex expression and match them up with a input string, then if they are the same, we will pass the validation check, and make a decision from there.

The Script

Our random string generator:

>>> import uuid
>>> import random
>>> letters = 'abcdefghijklmnopqrstuvwxyz'
>>> def generate_string():
...     random_letters = ''.join(random.choice(letters) for x in range(3))
...     response = 'my-random-' + random_letters + '-string_' + uuid.uuid4().hex
...     return response

Our validation check:

>>> import re
>>> def validation_check(input_string):
...     regex = re.compile('my-random-[a-z]{3}-string_[0-9a-z]{32}\Z', re.I)
...     match = regex.match(str(input_string))
...     return bool(match)

Doing the validation check against our data:

>>> mystring = generate_string()
>>> mystring

>>> validate = validation_check(mystring)
>>> if validate == True:
...     print('The string {} is valid'.format(mystring))
... else:
...     print('The string {} is not valid'.format(mystring))

the string my-random-ngt-string_6346145281738193742120539836241 is valid

The function checks for a strict 32 characters in the random hex number, if you had to randomize the length, you can always use this regex:

regex = re.compile('my-random-[a-z]{3}-string__[0-9]+', re.I)

Thank You

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