31 essential Python string methods, recommended to collect!

String is the basic data type in Python, and it is used in almost every Python program.

1. Slicing

slicing, taking out some elements from a list or tuple according to certain conditions (such as a specific range, index, split value)

s = ' hello '
s = s[:]
print(s)
#hello
s = ' hello '
s = s[3:8]
print(s)
# hello

2. strip ()

strip() method is used to remove specified characters (default is space or newline character) or character sequence at the beginning and end of a string.

s = ' hello '.strip()
print(s)
# hello
s = '###hello###'.strip()
print(s)
# ###hello###

When using the strip() method, spaces or newlines are removed by default, so the # sign is not removed.

You can add specified characters to the strip() method, as shown below.

s = '###hello###'.strip('#')
print(s)
# hello

In addition, when the specified content is not at the beginning and end, it will not be removed.

s = ' n t hellon'.strip('n')
print(s)
#
#hello
s = 'n t hellon'.strip('n')
print(s)
#hello

There is a space before the first n, so only the trailing newline character will be taken.

The last parameter of the strip() method is to strip all combinations of its values. You can see the following case.

s = 'www.baidu.com'.strip('cmow.')
print(s)
# baidu

The outermost first character and last character parameter values ​​will be stripped from the string. Characters are removed from the front until a string character is reached that is not contained in the character set.

A similar action will occur at the tail.

3. lstrip()

Remove the specified character (default is space or newline character) or character sequence on the left side of the string.

s = ' hello '.lstrip()
print(s)
# hello

Similarly, all strings contained in the character set on the left can be removed.

s = 'Arthur: three!'.lstrip('Arthur: ')
print(s)
# ee!

4, rstrip()

Remove the specified character (default is space or newline character) or character sequence on the right side of the string.

s = ' hello '.rstrip()
print(s)
#hello

5. removeprefix()

Function to remove prefix in Python3.9.

# python 3.9
s = 'Arthur: three!'.removeprefix('Arthur: ')
print(s)
# three!

Compared with strip(), the strings in the character set will not be matched one by one.

6. removesuffix()

Function to remove suffix in Python3.9.

s = 'HelloPython'.removesuffix('Python')
print(s)
# Hello

7. replace()

Replace the content in the string with the specified content.

s = 'string methods in python'.replace(' ', '-')
print(s)
# string-methods-in-python
s = 'string methods in python'.replace(' ', '')
print(s)
# stringmethodsinpython

8. re.sub()

re is a regular expression, sub is substitute, which means replacement.

re.sub is a relatively complicated replacement.

import re
s = "stringmethods in python"
s2 = s.replace(' ', '-')
print(s2)
# string----methods-in-python
s = "stringmethods in python"
s2 = re.sub("s+", "-", s)
print(s2)
# string-methods-in-python

Compared with replace(), using re.sub() for replacement operation is indeed more advanced.

9. split()

Split the string, and the final result is a list.

s = 'string methods in python'.split()
print(s)
# ['string', 'methods', 'in', 'python']

When the delimiter is not specified, it will be separated by spaces by default.

s = 'string methods in python'.split(',')
print(s)
# ['string methods in python']

In addition, you can also specify the number of times the string is separated.

s = 'string methods in python'.split(' ', maxsplit=1)
print(s)
# ['string', 'methods in python']

10. rsplit()

Separate the string starting from the right side.

s = 'string methods in python'.rsplit(' ', maxsplit=1)
print(s)
# ['string methods in', 'python']

11. join()

string.join(seq). Using string as the separator, combine all elements (string representations) in seq into a new string.

list_of_strings = ['string', 'methods', 'in', 'python']
s = '-'.join(list_of_strings)
print(s)
# string-methods-in-python
list_of_strings = ['string', 'methods', 'in', 'python']
s = ' '.join(list_of_strings)
print(s)
# string methods in python

12. upper()

Convert all letters in the string to uppercase.

s = 'simple is better than complex'.upper()
print(s)
# SIMPLE IS BETTER THAN COMPLEX

13. lower()

Convert all letters in the string to lowercase.

s = 'SIMPLE IS BETTER THAN COMPLEX'.lower()
print(s)
# simple is better than complex

14. capitalize()

Convert the first letter in the string to uppercase.

s = 'simple is better than complex'.capitalize()
print(s)
# Simple is better than complex

15. islower()

Determine whether all letters in the string are lowercase, if so, return True, otherwise return False.

print('SIMPLE IS BETTER THAN COMPLEX'.islower()) # False
print('simple is better than complex'.islower()) # True

16. isupper()

Determine whether all letters in the string are uppercase, if so, return True, otherwise return False.

print('SIMPLE IS BETTER THAN COMPLEX'.isupper()) # True
print('SIMPLE IS BETTER THAN complex'.isupper()) # False

17, isalpha()

If the string has at least one character and all characters are letters, return True, otherwise return False.

s = 'python'
print(s.isalpha())
# True
s = '123'
print(s.isalpha())
# False
s = 'python123'
print(s.isalpha())
# False
s = 'python-123'
print(s.isalpha())
# False

18, isnumeric()

If the string contains only numeric characters, return True, otherwise return False.

s = 'python'
print(s.isnumeric())
# False
s = '123'
print(s.isnumeric())
# True
s = 'python123'
print(s.isnumeric())
# False
s = 'python-123'
print(s.isnumeric())
# False

19, isalnum()

If there is at least one character in the string and all characters are letters or numbers, return True, otherwise return False.

s = 'python'
print(s.isalnum())
# True
s = '123'
print(s.isalnum())
# True
s = 'python123'
print(s.isalnum())
# True
s = 'python-123'
print(s.isalnum())
# False

20, count()

Returns the number of times the specified content appears in the string.

n = 'hello world'.count('o')
print(n)
# 2
n = 'hello world'.count('oo')
print(n)
# 0

21. find()

Check whether the specified content is included in the string. If so, return the starting index value, otherwise return -1.

s = 'Machine Learning'
idx = s.find('a')
print(idx)
print(s[idx:])
# 1
# achine Learning
s = 'Machine Learning'
idx = s.find('aa')
print(idx)
print(s[idx:])
# -1
# g

In addition, you can also specify the starting range.

s = 'Machine Learning'
idx = s.find('a', 2)
print(idx)
print(s[idx:])
# 10
# arning

22. rfind()

Similar to the find() function, returns the last occurrence of the string, or -1 if there is no match.

s = 'Machine Learning'
idx = s.rfind('a')
print(idx)
print(s[idx:])
# 10
# arning

23, startswith()

Check whether the string starts with the specified content, if so, return True, otherwise return False.

print('Patrick'.startswith('P'))
# True

24, endswith()

Check whether the string ends with the specified content, if so, return True, otherwise return False.

print('Patrick'.endswith('ck'))
# True

25. partition()

string.partition(str), a bit like a combination of find() and split().

Starting from the first position where str appears, divide the string string into a 3-element tuple (string_pre_str, str, string_post_str). If string does not contain str, then string_pre_str==string.

s = 'Python is awesome!'
parts = s.partition('is')
print(parts)
# ('Python ', 'is', ' awesome!')
s = 'Python is awesome!'
parts = s.partition('was')
print(parts)
# ('Python is awesome!', '', '')

26, center()

Returns a new string in which the original string is centered and filled with spaces to the length width.

s = 'Python is awesome!'
s = s.center(30, '-')
print(s)
# ------Python is awesome!------

27, ljust()

Returns a new string in which the original string is left-aligned and padded with spaces to length width.

s = 'Python is awesome!'
s = s.ljust(30, '-')
print(s)
# Python is awesome!------------

28, rjust()

Returns a new string with the original string right-aligned and padded with spaces to the length width.

s = 'Python is awesome!'
s = s.rjust(30, '-')
print(s)
# ------------Python is awesome!

29, f-Strings

f-string is the new syntax for formatting strings.

与其他格式化方式相比，它们不仅更易读，更简洁，不易出错，而且速度更快！

num = 1
language = 'Python'
s = f'{language} is the number {num} in programming!'
print(s)
# Python is the number 1 in programming!
num = 1
language = 'Python'
s = f'{language} is the number {num*8} in programming!'
print(s)
# Python is the number 8 in programming!

30、swapcase()

翻转字符串中的字母大小写。

s = 'HELLO world'
s = s.swapcase()
print(s)
# hello WORLD

31、zfill()

string.zfill(width)。

返回长度为width的字符串，原字符串string右对齐，前面填充0。

s = '42'.zfill(5)
print(s)
# 00042
s = '-42'.zfill(5)
print(s)
# -0042
s = '+42'.zfill(5)
print(s)
# +0042

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