Python Cookbook

Checking Whether a String Contains a Set of Characters

Credit: Jürgen Hermann, Horst Hansen

Problem

You need to check for the occurrence of any of a set of characters in a string.

Solution

The solution generalizes to any sequence (not just a string), and any set (any object in which membership can be tested with the in operator, not just one of characters):

def containsAny(str, set):
    """ Check whether sequence str contains ANY of the items in set. """
    return 1 in [c in str for c in set]

def containsAll(str, set):
    """ Check whether sequence str contains ALL of the items in set. """
    return 0 not in [c in str for c in set]

Discussion

While the find and count string methods can check for substring occurrences, there is no ready-made function to check for the occurrence in a string of a set of characters.

While working on a condition to check whether a string contained the special characters used in the glob.glob standard library function, I came up with the above code (with help from the OpenProjects IRC channel #python). Written this way, it really is compatible with human thinking, even though you might not come up with such code intuitively. That is often the case with list comprehensions.

The following code creates a list of 1/0 values, one for each item in the set:

[c in str for c in set]

Then this code checks whether there is at least one true value in that list:

1 in [c in str for c in set]

Similarly, this checks that no false values are in the list:

0 not in [c in str for c in set] ...