Master Python’s string Module: capwords, Template, and Performance Hacks

Importing the module

import string

capwords

The capwords function capitalizes the first letter of each word in a string, optionally using a custom separator.

def capwords(s, sep=None):
    return (sep or ' ').join(x.capitalize() for x in s.split(sep))

Example usage:

>> s = 'my name is python'
>>> capwords(s)
'My Name Is Python'

>>> s = 'my-name-is-python'
>>> capwords(s, '-')
'My-Name-Is-Python'

Alternative implementations using map and methodcaller:

def capwords1(s: str, seq: str=None) -> str:
    return (seq or ' ').join(map(str.capitalize, s.split(seq)))

from operator import methodcaller

def capwords2(s: str, seq: str=None) -> str:
    return (seq or ' ').join(map(methodcaller('capitalize'), s.split(seq)))

Performance comparison (run in IPython) shows the first custom version is slightly faster than the built‑in implementation, while the second custom version is slower:

text = "your time is limted, so don't waste it living someone else's lives" * 10000
%timeit capwords(text)   # 24.9 ms
%timeit capwords1(text)  # 22.1 ms
%timeit capwords2(text)  # 28.4 ms

Template

The Template class provides safe string interpolation using $ placeholders.

from string import Template
string = '姓名：$name 年龄：${age} 爱好：$hobby'
template = Template(string)

Substitution with a dictionary:

template.substitute({'name':'Python','age':30,'hobby':'all'})
# '姓名：Python 年龄：30 爱好：all'

Keyword‑argument substitution raises KeyError if a placeholder is missing; safe_substitute leaves missing placeholders unchanged:

template.safe_substitute(name='Python', age=30, hobb='all')
# '姓名：Python 年龄：30 爱好：$hobby'

Key class attributes of Template:

class Template(metaclass=_TemplateMetaclass):
    """A string class for supporting $-substitutions."""
    delimiter = '$'
    idpattern = r'(?a:[_a-z][_a-z0-9]*)'
    braceidpattern = None
    flags = _re.IGNORECASE

Custom subclass can override delimiter and idpattern:

class MyTemplate(Template):
    delimiter = '%'
    idpattern = '[_][a-z]+_[a-z]+'

Using the custom template:

s = '%_name_main %age'
template = MyTemplate(s)
template.safe_substitute(_name_main='Python', age=30)
# 'Python %age'

These examples demonstrate how to work with the string module’s utilities, compare implementations, and safely perform string interpolation.