CODEWITHSUNDEEP
pythonstringletters
Алексей Дарьев
Алексей Дарьев

Reputation: 21

python filter letters in a string

I need a command in python which filters the letters in a string but not deleting them for example:

string =raw_input("Enter the string:")
if string.startswith("a") and string.endswith("aaa"):
    print "String accepted"
else: print "String not accepted"
if "ba" in string:
    print "String accepted"
else :
    print "String is not accepted"

What should I add to ban other letters except a and b in the string

Upvotes: 2

Views: 441

Answers (5)

Steven Summers
Steven Summers

Reputation: 5384

Try something like this. It lets you set multiple letters, symbols, etc

valid_char = ['a', 'b']

def validate(s):
    for char in s:
        if char not in valid_char:
            return False
    return True

if validate(input("Enter the string:")):
    print('Sting Accepted')
else:
    print('Sting not Accepted')

Upvotes: 0

Anand S Kumar
Anand S Kumar

Reputation: 90889

You can use a set , convert your string to a set and check if its a subset of a set with only a and b. Example -

s = raw_input("Enter the string:")
validset = set('ab')
if set(s).issubset(validset):
    print "String accepted"
else: 
    print "String not accepted"

Demo -

>>> s = "abbba"
>>> validset = set(['a','b'])
>>> if set(s).issubset(validset):
...     print "String accepted"
... else: print "String not accepted"
... 
String accepted

>>> s = "abbbac"
>>> if set(s).issubset(validset):
...     print "String accepted"
... else: print "String not accepted"
... 
String not accepted

Or as indicated in the comments you can use set.issuperset() instead . Example -

s = raw_input("Enter the string:")
validset = set('ab')
if validset.issuperset(s):
    print "String accepted"
else: 
    print "String not accepted"

Upvotes: 1

machine yearning
machine yearning

Reputation: 10119

This is a good use of regular expressions:

import re
my_string = raw_input("Enter the string:")
if re.match('^[ab]+$', my_string):
    print "String accepted"
else :
    print "String is not accepted"

This will match strings which contain only the characters a and b, of non-zero length. If you want to match zero-length strings, use * instead of +.

Upvotes: 1

Astrogat
Astrogat

Reputation: 1625

You could use a regex to search for letters and combinations you want to filter.

^((?![abcd]).)*$ will match things that don't contain a, b, c or d.

Upvotes: 0

TigerhawkT3
TigerhawkT3

Reputation: 49318

You can simply replace them with the empty string and check whether there's anything left:

string = raw_input("Enter the string:")
if string.replace('a','').replace('b',''):
    print "String not accepted"
else:
    print "String accepted"

The original string string will not be modified.

Upvotes: 2

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