String Methods

String methods in Python are built-in functions that allow you to manipulate and analyze text data. These methods help you perform common operations such as searching, modifying, and formatting strings efficiently.

Commonly Used String Methods

1. str.upper() and str.lower():

   • Convert a string to uppercase or lowercase.
   • Example:

     text = "Hello, World!"
     upper_text = text.upper()  # "HELLO, WORLD!"
     lower_text = text.lower()  # "hello, world!"
     

2. str.capitalize() and str.title():

   • Capitalize the first letter of a string or capitalize the first letter of each word.
   • Example:

     text = "hello, world!"
     capitalized_text = text.capitalize()  # "Hello, world!"
     title_text = text.title()  # "Hello, World!"
     

3. str.strip(), str.lstrip(), and str.rstrip():

   • Remove leading and/or trailing whitespace (or other specified characters).
   • Example:

     text = "   Hello, World!   "
     stripped_text = text.strip()  # "Hello, World!"
     left_stripped = text.lstrip()  # "Hello, World!   "
     right_stripped = text.rstrip()  # "   Hello, World!"
     

4. str.replace():

   • Replace occurrences of a substring with another substring.
   • Example:

     text = "Hello, World!"
     replaced_text = text.replace("World", "Python")  # "Hello, Python!"
     

5. str.split() and str.join():

   • split(): Split a string into a list of substrings based on a delimiter.
   • join(): Join a list of strings into a single string with a specified delimiter.
   • Example:

     text = "Hello, World!"
     words = text.split(", ")  # ["Hello", "World!"]
     joined_text = " - ".join(words)  # "Hello - World!"
     

6. str.find() and str.index():

   • find(): Return the lowest index of the substring if found, otherwise return -1.
   • index(): Similar to find(), but raises a ValueError if the substring is not found.
   • Example:

     text = "Hello, World!"
     index = text.find("World")  # 7
     # index_not_found = text.index("Python")  # Raises ValueError
     

7. str.startswith() and str.endswith():

   • Check if a string starts or ends with a specified substring.
   • Example:

     text = "Hello, World!"
     starts_with = text.startswith("Hello")  # True
     ends_with = text.endswith("World!")  # True
     

8. str.count():

   • Count the number of occurrences of a substring in a string.
   • Example:

     text = "Hello, World! Hello again!"
     count = text.count("Hello")  # 2
     

9. str.isalpha(), str.isdigit(), and str.isalnum():

   • isalpha(): Check if the string consists only of alphabetic characters.
   • isdigit(): Check if the string consists only of digits.
   • isalnum(): Check if the string consists only of alphanumeric characters (letters and numbers).
   • Example:

     text_alpha = "Hello"
     text_digit = "12345"
     text_alnum = "Hello123"
     is_alpha = text_alpha.isalpha()  # True
     is_digit = text_digit.isdigit()  # True
     is_alnum = text_alnum.isalnum()  # True
     

10. str.center(), str.ljust(), and str.rjust():

    • Adjust the alignment of a string to be centered, left-justified, or right-justified within a given width.
    • Example:

      text = "Hello"
      centered = text.center(10, "-")  # "--Hello---"
      left_justified = text.ljust(10, "-")  # "Hello-----"
      right_justified = text.rjust(10, "-")  # "-----Hello"
      

Advanced String Methods

1. str.zfill():

   • Pad a string on the left with zeros until it reaches the specified length.
   • Example:

     text = "42"
     padded_text = text.zfill(5)  # "00042"
     

2. str.partition() and str.rpartition():

   • Split the string into a tuple with three parts: the part before the separator, the separator itself, and the part after the separator.
   • Example:

     text = "Hello, World!"
     parts = text.partition(", ")  # ("Hello", ", ", "World!")
     

3. str.casefold():

   • Return a case-insensitive version of the string, useful for caseless matching.
   • Example:

     text = "Hello, World!"
     casefolded_text = text.casefold()  # "hello, world!"