string

The string module provides useful constants for character classification and a Formatter class for custom string formatting. Unlike string methods that operate on string instances, these are module-level utilities that help with common string tasks.

String Constants

The module defines several constants containing useful character sets. These are handy for validation, parsing, and character classification.

import string

# Check what each constant contains
print(string.ascii_letters)
# abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

print(string.ascii_lowercase)
# abcdefghijklmnopqrstuvwxyz

print(string.ascii_uppercase)
# ABCDEFGHIJKLMNOPQRSTUVWXYZ

print(string.digits)
# 0123456789

print(string.hexdigits)
# 0123456789abcdefABCDEF

print(string.octdigits)
# 01234567

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

print(string.printable)
# 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

print(string.whitespace)
# 	



capwords()

The capwords() function capitalizes the first letter of each word in a string. It splits on whitespace, capitalizes each word, and joins them back.

Syntax

string.capwords(s, sep=None)

Parameters

Parameter	Type	Default	Description
s	str	—	The input string to process
sep	str	None	Separator used to split words. Defaults to whitespace

Examples

Basic usage

import string

result = string.capwords("hello world")
print(result)
# Hello World

Custom separator

import string

result = string.capwords("apple,banana,cherry", sep=",")
print(result)
# Apple,Banana,Cherry

Whitespace handling

import string

# Multiple spaces are treated as one split point
result = string.capwords("  multiple   spaces  ")
print(result)
# Multiple Spaces

Formatter Class

The Formatter class provides flexible string formatting. It implements the same format string syntax as the built-in str.format() method, but as a class you can subclass to customize behavior.

Syntax

class string.Formatter

Methods

Method	Description
format(format_string, *args, **kwargs)	Main API — formats the string with given arguments
vformat(format_string, args, kwargs)	Does the actual work, useful when passing a dict
parse(format_string)	Returns tuples of (literal_text, field_name, format_spec, conversion)
get_field(field_name, args, kwargs)	Resolves a field name to its value
get_value(key, args, kwargs)	Gets a positional or keyword argument by key

Examples

Basic formatting

import string

f = string.Formatter()
result = f.format("{0} {1}", "Hello", "World")
print(result)
# Hello World

Parsing format strings

import string

f = string.Formatter()
# parse() breaks a format string into its components
result = list(f.parse("Hello {0}, your score is {1}!"))
print(result)
# [('Hello ', '0', '', None), (', your score is ', '1', '', None), ('!', '', '', None)]

Custom formatting

import string

class MyFormatter(string.Formatter):
    def format_field(self, value, format_spec):
        # Custom: add brackets around formatted values
        return f"[{super().format_field(value, format_spec)}]"

f = MyFormatter()
result = f.format("{0:.2f}", 3.14159)
print(result)
# [3.14]

Common Patterns

Character class validation

import string

def is_ascii(s):
    """Check if string contains only ASCII characters."""
    return all(c in string.printable for c in s)

print(is_ascii("Hello World"))  # True
print(is_ascii("Héllo"))         # False
print(is_ascii("123"))           # True

Generating random strings

import random
import string

def generate_random_string(length=10, charset=string.ascii_letters):
    """Generate a random string from a character set."""
    return ''.join(random.choice(charset) for _ in range(length))

# Random alphanumeric string
print(generate_random_string(8))
# kR4mTqNp

# Random lowercase + digits (like a password)
print(generate_random_string(12, string.ascii_lowercase + string.digits))
# a7b3c9d2e1f4

Text cleaning

import string

def remove_punctuation(text):
    """Remove punctuation from text."""
    return text.translate(str.maketrans('', '', string.punctuation))

result = remove_punctuation("Hello, World! How are you?")
print(result)
# Hello World How are you

See Also

• re module
• textwrap
• difflib