How to check a string for specific characters?

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Question :

How to check a string for specific characters?

How can I check if a string has several specific characters in it using Python 2?

For example, given the following string:

The criminals stole $1,000,000 in jewels.

How do I detect if it has dollar signs (“$”), commas (“,”), and numbers?

Asked By: The Woo


Answer #1:

Assuming your string is s:

'$' in s        # found
'$' not in s    # not found

# original answer given, but less Pythonic than the above...
s.find('$')==-1 # not found
s.find('$')!=-1 # found

And so on for other characters.

… or

pattern = re.compile(r'd$,')
if pattern.findall(s):
    print('Not found')

… or

chars = set('0123456789$,')
if any((c in chars) for c in s):
    print('Not Found')

[Edit: added the '$' in s answers]

Answered By: dappawit

Answer #2:

user Jochen Ritzel said this in a comment to an answer to this question from user dappawit.
It should work:

('1' in var) and ('2' in var) and ('3' in var) ...

‘1’, ‘2’, etc. should be replaced with the characters you are looking for.

See this page in the Python 2.7 documentation for some information on strings, including about using the in operator for substring tests.

Update: This does the same job as my above suggestion with less repetition:

# When looking for single characters, this checks for any of the characters...
# ...since strings are collections of characters
any(i in '<string>' for i in '123')
# any(i in 'a' for i in '123') -> False
# any(i in 'b3' for i in '123') -> True

# And when looking for subsrings
any(i in '<string>' for i in ('11','22','33'))
# any(i in 'hello' for i in ('18','36','613')) -> False
# any(i in '613 mitzvahs' for i in ('18','36','613')) ->True
Answered By: Abbafei

Answer #3:

Quick comparison of timings in response to the post by Abbafei:

import timeit

def func1():
    phrase = 'Lucky Dog'
    return any(i in 'LD' for i in phrase)

def func2():
    phrase = 'Lucky Dog'
    if ('L' in phrase) or ('D' in phrase):
        return True
        return False

if __name__ == '__main__': 
    func1_time = timeit.timeit(func1, number=100000)
    func2_time = timeit.timeit(func2, number=100000)
    print('Func1 Time: {0}nFunc2 Time: {1}'.format(func1_time, func2_time))


Func1 Time: 0.0737484362111
Func2 Time: 0.0125144964371

So the code is more compact with any, but faster with the conditional.

EDIT : TL;DR — For long strings, if-then is still much faster than any!

I decided to compare the timing for a long random string based on some of the valid points raised in the comments:

# Tested in Python 2.7.14

import timeit
from string import ascii_letters
from random import choice

def create_random_string(length=1000):
    random_list = [choice(ascii_letters) for x in range(length)]
    return ''.join(random_list)

def function_using_any(phrase):
    return any(i in 'LD' for i in phrase)

def function_using_if_then(phrase):
    if ('L' in phrase) or ('D' in phrase):
        return True
        return False

if __name__ == '__main__':
    random_string = create_random_string(length=2000)
    func1_time = timeit.timeit(stmt="function_using_any(random_string)",
                               setup="from __main__ import function_using_any, random_string",
    func2_time = timeit.timeit(stmt="function_using_if_then(random_string)",
                               setup="from __main__ import function_using_if_then, random_string",
    print('Time for function using any: {0}nTime for function using if-then: {1}'.format(func1_time, func2_time))


Time for function using any: 0.1342546
Time for function using if-then: 0.0201827

If-then is almost an order of magnitude faster than any!

Answered By: Jesuisme

Answer #4:

This will test if strings are made up of some combination or digits, the dollar sign, and a commas. Is that what you’re looking for?

import re

s1 = 'Testing string'
s2 = '1234,12345$'

regex = re.compile('[0-9,$]+$')

if ( regex.match(s1) ):
   print "s1 matched"
   print "s1 didn't match"

if ( regex.match(s2) ):
   print "s2 matched"
   print "s2 didn't match"
Answered By: ajwood

Answer #5:

My simple, simple, simple approach! =D


string_to_test = "The criminals stole $1,000,000 in jewels."
chars_to_check = ["$", ",", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
for char in chars_to_check:
if char in string_to_test:
print("Char "" + char + """" detected!"")

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