Testing for non-printable characters

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October 13th, 2004, 11:53 AM

lauramccord

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Testing for non-printable characters

Hi,

I am trying to figure out how to test if there are non-printable characters in a given string.

For example,

givenString = 'test characters'
for c in givenString:
if (c == .....):
return "not a valid string"

So in my if(c == ...) I am not sure what to replace the ..... with.

Any ideas?

-Laura

October 13th, 2004, 12:43 PM

Scorpions4ever

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The string module has printable, which contains a list of printable characters.

Code:

import string

if c in string.printable:

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October 13th, 2004, 12:59 PM

lauramccord

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It is not working. This is what I have

Code:

 
import string
passwd1 = 'string 123'
check = 0

for c in passwd1:
 if c in string.printable:
  check = check + 1
 else:
  print "Password cannot contain non-printable chracters"

print check

check returns 10 which means it is not triggering the error message for the space in between string and 123. I tried putting a tab in between the string also and it didn't work.

Am I forgetting something?
-Laura

October 13th, 2004, 01:05 PM

Scorpions4ever

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This is because string.printable considers whitespace as printable characters as well.
http://docs.python.org/lib/module-string.html
If you want to exclude whitespace, you can check if c is in string.letters, string.punctuation and string.digits.

October 13th, 2004, 01:08 PM

lauramccord

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Ok. I think I should have used string.whitespace

This is at least a start for me. But, in actuality I need to put more restrictions on my string. For example, it must contain at least 1 special character (! @ # $ & ^) but it cannot contain (\ / |). Plus, the string must have at least one digit along with no whitespace characters.

I know that I may need to create a regular expression but I am not that confident on how to build it with all of these restrictions.

Thanks for you help.

-Laura

October 13th, 2004, 01:44 PM

netytan

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If you deside to give the regex ago (and i think its really you're best bet here,) then you might want to check out Kodos: the Python regular expression debugger. I love this thing, it just makes working with regex and Python fun.

http://kodos.sourceforge.net/

Note: Since Python and perl use the same regex you could always use this to test regex for perl too. Alternativly, if you can find a regex that already does what you want in perl. You should be able to use that

.

Take care,

Mark.

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October 13th, 2004, 01:57 PM

Scorpions4ever

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You could also take the easy way out and perform several checks on the string as you go and then check flags at the end to see if the string passes your requirements.

Code:

#!/usr/bin/env python                 
import string

def checkstr(param):
    specialcount = 0
    bad = 0
    goodsyms = ['!', '@', '#', '$', '&', '^']
    for c in param:
        if not(c in string.printable):
            bad = 1
            break

        if c in string.punctuation:
            if c in goodsyms:
                specialcount += 1
            else:
                bad = 1
                break

    if bad == 1 or specialcount != 1:
        return 0
    else:
        return 1


teststr = "This is a big string!"
print checkstr(teststr)
teststr = "This is a big string with no punctuation"
print checkstr(teststr)
teststr = "This is a big string with extra punctuation!!$"
print checkstr(teststr)
teststr = "This is a big string with bad punctuation/|?"
print checkstr(teststr)

This approach doesn't use regexs and is pretty simple to understand as well

October 14th, 2004, 01:05 PM

lauramccord

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Yes, that is alot easier.

Thanks for your help
Laura

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