Python String Methods, with Examples

Detailed explanation of Python string method: efficient processing of text data

Python provides a rich string method for handling string objects such as formatting, searching, and modifying without changing the original string because strings are immutable. This article will introduce some commonly used Python string methods and explain them in combination with examples.

Characteristics of strings

Stands are an integral part of programming languages ​​and one of the most commonly used data types in Python. They are sequences of immutable Unicode characters that can be enclosed in single, double or triple quotation marks. Immutability means that once a string is created, it cannot be modified directly; any modification operation will create a new string object.

Example string in Python:

greeting = "Hello, World!"

Note: Unlike Java or other programming languages, Python does not support character data types. So a single character enclosed in quotes, such as 'c', is still a string.

Overview of string methods

Since strings are treated as sequences in Python, they implement all sequence operations such as joins, slices, etc.:

>>> word = 'golden'
>>> len(word)
6
>>> word + 'age'
'goldenage'
>>> 'la' * 3
'lalala'
>>>

In addition to sequence operations, there are many other additional methods related to string objects. These methods can be used to format strings, search for substrings in another string, trim spaces, perform certain checks on a given string, and so on.

It should be noted that these string methods do not modify the original string; since strings are immutable in Python, strings cannot be modified directly. Most string methods only return modified string copies or boolean values.

The following is a detailed introduction to some Python string methods, accompanied by examples.

Method to return a modified copy of the string

• str.capitalize(): Converts the first character of the string to uppercase and the rest to lowercase.

  Example:

  >>> "i Enjoy traveling. Do you?".capitalize()
  'I enjoy traveling. do you?'
  >>>

• str.center(width[, fillchar]): Returns a centered string, filled with the given fillchar and width. If width is less than or equal to the string length, the original string is returned.

  Example:

  >>> sentence = 'i Enjoy traveling. Do you?'
  >>> len(sentence)
  26
  >>> sentence.center(31)
  '  i Enjoy traveling. Do you? '
  >>> sentence.center(30)
  ' i Enjoy traveling. Do you? '

• str.encode(encoding='utf-8', errors='strict'): Returns a string encoded as bytes.

  By default, the string passed to the function is encoded as utf-8, and if an error occurs, a UnicodeEncodeError exception will be raised. The errors keyword parameter specifies how to handle errors, such as strict throws an exception, ignore ignores any errors encountered, etc. There are a few other coding options available.

  Example:

  greeting = "Hello, World!"

• *`str.format(args, kwargs)`: Returns a copy of the string in which each substitute field is replaced by the string value of the corresponding parameter.

  Example:

  >>> word = 'golden'
  >>> len(word)
  6
  >>> word + 'age'
  'goldenage'
  >>> 'la' * 3
  'lalala'
  >>>

• str.lower(): Convert all uppercase characters in a string to lowercase.

  Example:

  >>> "i Enjoy traveling. Do you?".capitalize()
  'I enjoy traveling. do you?'
  >>>

• str.removeprefix(prefix, /): Removes the specified prefix at the beginning of the string, and returns the original string if the prefix cannot be found.

  Example:

  >>> sentence = 'i Enjoy traveling. Do you?'
  >>> len(sentence)
  26
  >>> sentence.center(31)
  '  i Enjoy traveling. Do you? '
  >>> sentence.center(30)
  ' i Enjoy traveling. Do you? '

• str.removesuffix(suffix, /): Removes the specified suffix at the end of the string, and returns the original string if the suffix cannot be found.

  Example:

  >>> sentence = "i Enjoy traveling. Do you, 山本さん?"
  >>> sentence.encode()
  b'i Enjoy traveling. Do you, \xe5\xb1\xb1\xe6\x9c\xac\xe3\x81\x95\xe3\x82\x93?'
  >>> sentence.encode(encoding='ascii')
  Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
  UnicodeEncodeError: 'ascii' codec can't encode characters in position 27-30: ordinal not in range(128)
  >>> sentence.encode(encoding='ascii', errors='replace')
  b'i Enjoy traveling. Do you, ?????'

• str.replace(old, new[, count]): Replace all substrings that appear in the string with old. If the new parameter is provided, only the count occurrence substrings are replaced. count

  Example:

  >>> "I bought {0} apples and the cost {1:.2f} Ghana cedis.".format(2, 18.70)
  'I bought 2 apples and the cost 18.70 Ghana cedis.'
  >>> "My name is {first_name}, and I'm a {profession}.".format(first_name='Ben', profession='doctor')
  "My name is Ben, and I'm a doctor."
  >>>

• str.strip([chars]): Returns a new string where the characters specified at the beginning and end of the original string have been removed. If the parameter is not provided, spaces are removed by default. chars

  Example:

  >>> 'i Enjoy traveling. Do you?'.lower()
  'i enjoy traveling. do you?'
  >>>

• str.title(): capitalizes the first letter of each word in the string and lowercase the rest of the letters.

  Example:

  >>> 'i Enjoy traveling. Do you?'.removeprefix('i')
  ' Enjoy traveling. Do you?'
  >>>

• str.upper(): Convert all characters in a string to uppercase.

  Example:

  >>> 'i Enjoy traveling. Do you?'.removesuffix('Do you?')
  'i Enjoy traveling. '
  >>>

Methods to concatenate and split strings

• str.join(iterable): Concatenate the string in the iterable object into a new string. If the iterable object contains non-string values, a exception is thrown. TypeError

  Example:

  >>> 'i Enjoy traveling. Do you?'.replace('Enjoy','dislike')
  'i dislike traveling. Do you?'
  >>> 'Things fall apart'.replace('a','e',1)
  'Things fell apart'
  >>>

• str.split(sep=None, maxsplit=-1): Split the string into a list according to the specified separator.

  Example:

  >>> word1 = ' whitespace '.strip()
  >>> word1
  'whitespace'
  >>> word2 = 'exercise'.strip('e')
  >>> word2
  'xercis'
  >>> word3 = 'chimpanze'.strip('acepnz')
  >>> word3
  'him'
  >>>

How to query strings

• str.count(sub[, start[, end]]): Returns the number of times the substring appears in the string. sub

  Example:

  >>> 'i Enjoy traveling. Do you?'.title()
  'I Enjoy Traveling. Do You?'
  >>>

• str.find(sub[, start[, end]]): Returns the index of the location where the substring appears for the first time in the string. If the substring is not found, return -1. sub

  Example:

  >>> 'i Enjoy traveling. Do you?'.upper()
  'I ENJOY TRAVELING. DO YOU?'
  >>>

• str.index(sub[, start[, end]]): Returns the index of the location where the substring appears for the first time in the string. If the substring is not found, a sub exception is thrown. ValueError

  Example:

  >>> words = ["Accra", "is", "a", "beautiful", "city"]
  >>> ' '.join(words)
  'Accra is a beautiful city'
  >>> names = ['Abe', 'Fred', 'Bryan']
  >>> '-'.join(names)
  'Abe-Fred-Bryan'
  >>>

Methods to return boolean values

• str.endswith(suffix[, start[, end]]): Returns suffix if the string ends with the specified True; otherwise, return False.

  Example:

  greeting = "Hello, World!"

• str.isalnum(): Returns True if the string contains alphanumeric characters and has at least one character; otherwise returns False.

  Example:

  >>> word = 'golden'
  >>> len(word)
  6
  >>> word + 'age'
  'goldenage'
  >>> 'la' * 3
  'lalala'
  >>>

• str.isalpha(): Returns True if all characters in a string are letters and have at least one character; otherwise, return False.

  Example:

  >>> "i Enjoy traveling. Do you?".capitalize()
  'I enjoy traveling. do you?'
  >>>

• str.isascii(): Returns True if all characters in the string are ASCII characters or the string is empty; otherwise returns False.

  Example:

  >>> sentence = 'i Enjoy traveling. Do you?'
  >>> len(sentence)
  26
  >>> sentence.center(31)
  '  i Enjoy traveling. Do you? '
  >>> sentence.center(30)
  ' i Enjoy traveling. Do you? '

• str.isdecimal(): Returns True if the string contains all decimal characters and has at least one character; otherwise returns False.

  Example:

  >>> sentence = "i Enjoy traveling. Do you, 山本さん?"
  >>> sentence.encode()
  b'i Enjoy traveling. Do you, \xe5\xb1\xb1\xe6\x9c\xac\xe3\x81\x95\xe3\x82\x93?'
  >>> sentence.encode(encoding='ascii')
  Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
  UnicodeEncodeError: 'ascii' codec can't encode characters in position 27-30: ordinal not in range(128)
  >>> sentence.encode(encoding='ascii', errors='replace')
  b'i Enjoy traveling. Do you, ?????'

• str.isnumeric(): Returns True if the string contains all numeric characters and has at least one character; otherwise returns False.

  Example:

  >>> "I bought {0} apples and the cost {1:.2f} Ghana cedis.".format(2, 18.70)
  'I bought 2 apples and the cost 18.70 Ghana cedis.'
  >>> "My name is {first_name}, and I'm a {profession}.".format(first_name='Ben', profession='doctor')
  "My name is Ben, and I'm a doctor."
  >>>

• str.islower(): Returns True if all characters in a string are lowercase and have at least one character; otherwise, return False.

  Example:

  >>> 'i Enjoy traveling. Do you?'.lower()
  'i enjoy traveling. do you?'
  >>>

• str.isupper(): Returns True if all characters in a string are capitalized and have at least one character; otherwise returns False.

  Example:

  >>> 'i Enjoy traveling. Do you?'.removeprefix('i')
  ' Enjoy traveling. Do you?'
  >>>

• str.startswith(prefix[, start[, end]]): Returns prefix if the string begins with the specified True; otherwise, return False.

  Example:

  >>> 'i Enjoy traveling. Do you?'.removesuffix('Do you?')
  'i Enjoy traveling. '
  >>>

Byte method (bytes.decode())

• bytes.decode(encoding='utf-8', errors='strict'): Decode the bytes into a string.

  By default, the encoding is 'utf-8', and if an error occurs, a UnicodeDecodeError exception will be raised. strict, ignore and replace are error keyword parameters that specify how exceptions are handled.

  Example:

  >>> 'i Enjoy traveling. Do you?'.replace('Enjoy','dislike')
  'i dislike traveling. Do you?'
  >>> 'Things fall apart'.replace('a','e',1)
  'Things fell apart'
  >>>

Summary

Proficiency in Python string methods is essential for efficient processing of text data. Python provides a wealth of tools to easily perform string manipulation and improve programming efficiency.

Challenge

Try to predict the output of the following code:

>>> word1 = ' whitespace '.strip()
>>> word1
'whitespace'
>>> word2 = 'exercise'.strip('e')
>>> word2
'xercis'
>>> word3 = 'chimpanze'.strip('acepnz')
>>> word3
'him'
>>>

You can run code in a Python interactive environment to verify your answer.

(The FAQs part is omitted because it is too long and does not match the pseudo-original goal. The FAQs content can be added elsewhere as needed.)

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