如何检查一个字符串是否只包含小写字母和数字？

Question

How can I check if a string contains only numbers and lower case letters?

I only managed to check if it contains numbers and lower case letters and doesn't contain upper case letters but I don't know how to check that it doesn't contain any symbols as ^&*(% etc..

if(any(i.islower() for i in password) and any(i.isdigit() for i in password) and not any(i.isupper() for i in password)):

EDIT: so apparently I need to do this without using any loops and mainly using functions like.islower(), .isdigit(), isalnum() etc.. and I have no idea how I can check if a string contains lower case letters and numbers only, without using loops or something that will check every single char in the string. we only started to learn the basics in python so they told us we can't use "for" and all that even if I know what it does.. now I can check if an entire string is only digits or lower/upper case letters but I don't know how to check the two conditions mentioned above in the simplest way possible

Answer 1

How about use regex :

>>> def is_digit_and_lowercase_only(s):
        return re.match("^[\da-z]+$", s)
>>> print is_digit_and_lowercase_only("dA")
None
>>> print is_digit_and_lowercase_only("adc87d6f543sc")
<_sre.SRE_Match object at 0x107c46988>

It'll return None if match failed, so you can use it with if .

Answer 2

What about:

if  for c in password:

after all, you want to check that all characters are either a digit or lowercase letters. So for all characters c , that character is c.isdigit() or c.islower() . Now an all(..) takes as input an iterable of values and checks if the truthiness of all these values is True . So from the moment there is one digit that does not satisfies our condition, the all(..) will return False .

Mind however that all(..) is True if there are no elements . Indeed if the password is the empty string, all the characters satisfy this condition, since there are no characters.

EDIT :

In case you want to check that the password contains both digits and lowercase characters, you can alter the condition to:

if all(c.isdigit() or c.islower() for c in password) 
       
       :

Now the check will only succeed if there are at least two characters in password : a lower and a digit.

Answer 3

Another solution is to count the letters of each type and make sure they're not zero (in this context True equates to 1 and False to 0):

def validate_password(password):
    """
    Return True if password contains digits and lowercase letters
    but nothing else and is at least 8 characters long; otherwise
    return False.

    """

    ndigits = sum(c.isdigit() for c in password)
    nlower = sum(c.islower() for c in password)
    password_length = len(password)
    return (password_length > 7 and ndigits and nlower and
            (ndigits+nlower)==password_length)

Answer 4

Define a function that applies your rules using sets for membership testing .

import string
lower = set(string.ascii_lowercase)
digits = set(string.digits)
def valid(s):
    '''Test string for valid characters, and composition'''

    s = set(s)
    invalid = s.difference(lower, digits)
    both = s.intersection(lower) and s.intersection(digits)
    return bool(both and not invalid)

Usage:

>>> valid('12234')
False
>>> valid('abcde')
False
>>> valid('A123')
False
>>> valid('a$1')
False
>>> valid('1a')
True
>>>

Answer 5

simplest answer from the top of my head:

if str1 == str1.lower():
    # string is only lower case
else:
    # string is not only lower case

Answer 6

You can use isdigit() or islower() method to check string contains only numbers and lower case letters

import string
input_str=raw_input()


for ch in input_str:

    if  ch.isdigit() or  ch.islower():
        output_str=True

    else:
        output_str=False
        break   

print output_str

Answer 7

In [87]: '123anydigitorletterorevenunicodeßßидажелатиница'.isalnum()
Out[87]: True

In [88]: '123anydigitorletterorevenunicodeßßидажелатиница'.islower()
Out[88]: True

So the solution is

if password.islower() and password.isalnum():
    ...some code...

I can not figure out what for to iterate the string