Punctuation

A Python string may contain letters, whitespace, numbers, and punctuation. Punctuation characters include commas and periods and semicolons.

With Python, we can access the string.punctuation constant. This contains all the common punctuation characters. It can be tested and used in programs.

In operator use

Here we use the in-operator on the string.punctuation constant. This allows us to test whether a char in a string is a punctuation character.

import string

# An input string.
name = "hey, my friend!"

for c in name:
    # See if the char is punctuation.
    if c in string.punctuation:
        print("Punctuation: " + c)
Punctuation: ,
Punctuation: !

Loop example

In this example we use a for-in loop over the string.punctuation characters. We print each character with surrounding brackets.

import string

# Display punctuation.
for c in string.punctuation:
    print("[" + c + "]")
[!]
["]
[#]
[$]
[%]
[&]
[']
[(]
[)]
[*]
[+]
[,]
[-]
[.]
[/]
[:]
[;]
[<]
[=]
[>]
[?]
[@]
[[]
[\]
[]]
[^]
[_]
[`]
[{]
[|]
[}]
[~]

Remove punctuation

With the "in" operator and the string.punctuation constant, we can remove all punctuation chars from a string.

import string

def remove_punctuation(value):
    result = ""
    for c in value:
        # If char is not punctuation, add it to the result.
        if c not in string.punctuation:
            result += c
    return result

# Test our method.
temp = "hello, friend!... welcome."
print(temp)
print(remove_punctuation(temp))
hello, friend!... welcome.
hello friend welcome

Whitespace

Let us look at another occasionally-helpful constant in the string module: string.whitespace. This too can be looped over or tested.

import string

print(" " in string.whitespace)
print("\n" in string.whitespace)
print("X" in string.whitespace)
True
True
False

For performance, the in-operator is fast. But it will not outperform a specialized lookup table. We could use a dictionary to store a value indicating whether a char is punctuation or not.

Python contains many helpful constants in its string module. For example, we can test whitespace, digits, punctuation. We avoid writing these characters out in special code.