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String Operations

Reverse a String​

a = "hello world"
print(a[::-1])

String Concatenation​

  • In java string concatenation is O(n**2) thus you should use StringBuilder.
  • In python string concatenation is O(n), because the underline cpython handles the string builder.
  • In python string is immutable, thus you can not do string replacement in place.
    • Instead convert it into a list.

String Property Checking​

  • isupper to check if a string is all uppercase
  • islower to check if a string is all lowercase
  • isnumeric to check if a string is all numeric
  • isalpha to check is a string is all alphabet
  • isalnum to check if a string is all numeric and alphabet
  • isspace to check is a string is all space/empty
print("USA".isupper()) #true

print("b".islower()) #true
print("Bc".islower()) #false

print("123".isnumeric()) #true

print("abc".isalpha()) #true
print("ab c".isalpha()) #false

print("abc123".isalnum()) #true

print("".isspace()) #false
print(" ".isspace()) #true
print(" \t".isspace()) #true

String Formatting​

print(f"The solution to 24 + 24 is {24 + 24}")

Strip​

  • The strip() method returns a copy of the string by removing both the leading and the trailing characters (based on the string argument passed).
" hello ".strip() #removed the white spaces output = hello

"##hello##".strip('#') #removed the #s at the start end end output = hello

"www.hello.com".strip('wcom')  #removed wcom from the string output = .hello.
"hello python".removeprefix("hello")  #output = python

"hello python".removesuffic("python") #output = hello

Replace​

  • The replace() method replaces a specified phrase with another specified phrase.
"hello world python".replace(" ", "-") #'hello-world-python'

Split​

  • The split() method splits a string into a list. You can specify the separator, default separator is any whitespace.
"hello world python".split() #['hello', 'world', 'python']

"www.python.com".split(".") #['www', 'python', 'com']

Join​

  • The join() method takes all items in an iterable and joins them into one string. A string must be specified as the separator.
a = ["hello", "python"]

"".join(a)  #hellopython

" ".join(a) #hello python

"-".join(a)  #hello-python

Count​

  • The count() method returns the number of elements with the specified value.
"hello world".count('l') #3

Find​

  • The find() method finds the first occurrence of the specified value. The find() method returns -1 if the value is not found.
"hello world".find('l') #2

"hello world".find("l", 2) #3 starts looking from index 2

"hello world".rfind('l') #9 starts looking from the end

Zfill​

  • The zfill() method adds zeros (0) at the beginning of the string, until it reaches the specified length.
"43".zfill(5) #00042
"-43".zfill(5) #-0042