String Methods Extended

The string data type has a lot of useful built-in methods that can help us solve more complex problems.

Removing Leading and/or Trailing Spaces

These methods do not remove spaces within the text.

string_data.strip()

• Returns a string that loses all leading and trailing white spaces

string_data.lstrip()

• Returns a string that loses all leading white spaces

string_data.rstrip()

• Returns a string that loses all trailing white spaces

# Strip() Examples

word1 = '   h ello   '
# 3 spaces then h ello then 3 spaces
print('word1.lstrip():', word1.lstrip(), 'world.')
print('word1.rstrip():', word1.rstrip(), 'world.')
print('word1.strip():', word1.strip(), 'world.')

word1.lstrip(): h ello    world.
word1.rstrip():    h ello world.
word1.strip(): h ello world.

Using replace()

replace() is a powerful function helps us modify a string by targeting a pattern.

string_data.replace(old_str, new_str, limit)

• Returns a new string that replaces all instances of the old_str with the new_str

• Limit (optional argument) doesn’t have to be set, if it is set, it will only apply the replace method based on the limit

• Therefore, this method can either use either 2 or 3 arguments

# Using replace() examples

word = 'Hello World'
test1 = word.replace('l', 'L')
print('test1:', test1)

test2 = word.replace('l', 'o', 2)
print('test2:', test2)

test3 = word.replace('Hello','Goodbye')
print('test3:', test3)

test4 = word.replace(' ', '')
print('test4:', test4)

test1: HeLLo WorLd
test2: Heooo World
test3: Goodbye World
test4: HelloWorld

Using startswith() and endswith()

String methods that can check the start or the end of a string.

string_data.startswith('pattern', start_index, end_index) string_data.endswith('pattern', start_index, end_index)

• Both of these methods return either True/False

• It looks for the string pattern argument either at the start or the end.

• The indexes of start and/or end are both optional

  • they are integer based arguments

# startswith() & endswith() examples

word = 'Hello World'

print("word.startswith('Hell'):", word.startswith('Hell')) # True
print("word.endswith('rld'):", word.endswith('rld')) # True

print("word.endswith('!'):", word.endswith('!')) # False
print("word.startswith('h'):", word.startswith('h')) # False

print("word.startswith(' ',5):", word.startswith(' ',5)) # True
print("word.endswith('or', 2, 9):", word.endswith('or', 2, 9)) # True because word[2:9] → ‘llo wor’

word.startswith('Hell'): True
word.endswith('rld'): True
word.endswith('!'): False
word.startswith('h'): False
word.startswith(' ',5): True
word.endswith('or', 2, 9): True

Items in a Sequence to String

str_data.join(iterable_data)

• the join() method returns a new string that combines all items in the sequence/iterable_data separated by the str_data provided

• Each item in the sequence/iterable data must be a string type

# .join() example

new_str = ', '.join(['1', '2', '3']) # new_str is: “1, 2, 3”
new_str2 = ' '.join('helloworld') # new_str2: “h e l l o w o r l d”

print(new_str)
print(new_str2)

1, 2, 3
h e l l o w o r l d

String to a List

There are many ways to convert a string data into a list.

list() function

• This function allows to convert a string to a list

• Each individual characters will be separated as a single item in the list

sorted() function

• This function will sort the given string in ASCII order

• The function will return a list

• Each individual character in the string will be an item in the list

Controlled Way to convert a string to a list: split()

str_data.split('pattern', numberOfTime)

• The split() method separates a string into a list

• Both arguments are optional, and when they are not specified: they will separate by spaces

  • pattern : this looks for a pattern to separate each items by

  • numberOfTime : this integer sets how many times to separate the string

# String to a List examples

phrase1 = 'Hello World!'
print(list(phrase1))

phrase2 = 'Mr. Park'
print(sorted(phrase2))
print('-'*64)

# Using .split()
result1 = 'hello world'.split()
print('result1:', result1)

result2 = 'a,b,c,d,e'.split(',')
print('result2:', result2)

result3 = '1$2$3$4$5'.split('$',2)
print('result3:', result3)

['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!']
[' ', '.', 'M', 'P', 'a', 'k', 'r', 'r']
----------------------------------------------------------------
result1: ['hello', 'world']
result2: ['a', 'b', 'c', 'd', 'e']
result3: ['1', '2', '3$4$5']