Python Data Type: String

In Python, a string is a sequence of characters enclosed in quotes. Strings are a versatile and commonly used data type.

Creating Strings

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Strings can be created using:

• Single Quotes (‘):

  Copysingle_quote = 'Hello'

• Double Quotes (“):

  Copydouble_quote = "World"

• Triple Quotes (”’ or “””):

  Used for multi-line strings. Also serves as docstrings for documentation.

  Copymulti_line = '''This is a multi-line string.'''

 

Accessing Strings

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Strings are indexed and immutable. You can access individual characters or substrings using:

• Indexing: Access individual characters using positive or negative indices.

  Copys = "Python"
  print(s[0]) # Output: 'P' (first character)
  print(s[-1]) # Output: 'n' (last character)
  

• Slicing: Extract substrings using [start:end:step].

  Copys = "Python"
  print(s[0:3]) # Output: 'Pyt' (characters from index 0 to 2)
  print(s[:3]) # Output: 'Pyt' (start defaults to 0)
  print(s[3:]) # Output: 'hon' (end defaults to length)
  print(s[::2]) # Output: 'Pto' (every 2nd character)
  

 

String Operations

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Operation	Description	Example	Output
Concatenation	Combine strings	Hello’ + ‘ World’	Hello World’
Repetition	Repeat a string	Hi’ * 3	HiHiHi’
Length	Get string length	len(‘Hello’)	5
Membership	Check substring existence	P’ in ‘Python’	TRUE

 

Common String Methods

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• Changing Case:

  Copys = "Python"
  print(s.lower()) # Output: 'python'
  print(s.upper()) # Output: 'PYTHON'
  print(s.capitalize()) # Output: 'Python'
  print(s.title()) # Output: 'Python'
  print(s.swapcase()) # Output: 'pYTHON'
  

• Trimming Whitespace:

  Copys = " Hello World "
  print(s.strip()) # Output: 'Hello World'
  print(s.lstrip()) # Output: 'Hello World '
  print(s.rstrip()) # Output: ' Hello World'
  

• Finding and Replacing:

  Copys = "Hello World"
  print(s.find('World')) # Output: 6 (start index of 'World')
  print(s.replace('World', 'Python')) # Output: 'Hello Python'
  

• Splitting and Joining:

  Copys = "apple,banana,cherry"
  print(s.split(',')) # Output: ['apple', 'banana', 'cherry']
  fruits = ['apple', 'banana', 'cherry']
  print(','.join(fruits)) # Output: 'apple,banana,cherry'
  

• Checking Content:

  Copys = "Python3"
  print(s.isalpha()) # Output: False (contains a digit)
  print(s.isdigit()) # Output: False
  print(s.isalnum()) # Output: True (letters and digits only)
  print(s.islower()) # Output: False
  print(s.isupper()) # Output: False
  

 

String Formatting

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• f-strings (Recommended, Python 3.6+):

  Copyname = "Alice"
  age = 30
  print(f"My name is {name} and I am {age} years old.")
  # Output: My name is Alice and I am 30 years old.
  

• str.format():

  Copyprint("My name is {} and I am {} years old.".format(name, age))
  # Output: My name is Alice and I am 30 years old.
  

• % Formatting:

  Copyprint("My name is %s and I am %d years old." % (name, age))
  # Output: My name is Alice and I am 30 years old.
  

 

Escape Sequences

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Special characters in strings can be represented using escape sequences:

Escape Sequence	Description	Example	Output
\’	Single quote	It\’s nice’	It’s nice’
\”	Double quote	“\”Hello\””	“Hello”‘
\\	Backslash	“C:\\path”	C:\path’
\n	Newline	“Hello\nWorld”	Multi-line
\t	Tab	“Hello\tWorld”	Hello World’

 

Raw Strings

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• Use r or R before a string to ignore escape sequences:

  Copypath = r"C:\new_folder\file.txt"
  print(path) # Output: C:\new_folder\file.txt
  

 

Immutability

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• Strings are immutable, meaning their contents cannot be changed. Operations like concatenation or slicing create a new string.

  Copys = "Hello"
  s[0] = "J" # Error: 'str' object does not support item assignment
  s = "Jello" # Reassigning creates a new string