1. String Methods (Built-in Functions)

1. Basic Operations:

   • len(s): Get the length of a string.

   • s[i]: Access the character at index i.

2. Case Handling:

   • s.lower(), s.upper(): Convert to lowercase/uppercase.

   • s.capitalize(), s.title(): Capitalize the first character or each word.

   • s.swapcase(): Swap lowercase to uppercase and vice versa.

3. String Search and Matching:

   • s.find(sub): Returns the first occurrence of sub or -1 if not found.

   • s.rfind(sub): Like find, but searches from the end.

   • s.count(sub): Count occurrences of a substring.

4. String Manipulation:

   • s.strip(), s.lstrip(), s.rstrip(): Remove whitespace or specified characters.

   • s.replace(old, new): Replace all occurrences of old with new.

   • s.split(sep): Split a string into a list of substrings.

   • 'sep'.join(iterable): Join elements of an iterable with a string.

5. Validation:

   • s.isdigit(), s.isalpha(), s.isalnum(): Check if the string is all digits, letters, or alphanumeric.

   • s.isspace(): Check if the string is only whitespace.

6. Slicing and Reversing:

   • s[start:end:step]: Slice a string.

   • s[::-1]: Reverse a string.

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2. Libraries for String Manipulation

1. re (Regular Expressions):

   • Use for pattern matching and advanced text processing.

   • Common methods:

     • re.match(): Match a pattern at the start of a string.

     • re.search(): Search for a pattern anywhere in the string.

     • re.findall(): Find all occurrences of a pattern.

     • re.sub(): Replace matches with a substring.

   • Example:

       import re
       re.findall(r'\d+', 'abc123def456')  # ['123', '456']
     

2. collections:

   • collections.Counter:

     • Count the frequency of characters or substrings.

     • Example:

         from collections import Counter
         Counter("aabbcc")  # Counter({'a': 2, 'b': 2, 'c': 2})
       

3. string (String Constants):

   • Provides constants like string.ascii_letters, string.digits, string.punctuation.

   • Example:

       import string
       print(string.ascii_lowercase)  # abcdefghijklmnopqrstuvwxyz
     

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3. Common Patterns to Know

1. Check for Palindromes:

    def is_palindrome(s):
        s = s.lower().replace(" ", "")
        return s == s[::-1]
   

2. Anagram Checking:

    def is_anagram(s1, s2):
        return sorted(s1) == sorted(s2)
   

3. Longest Substring without Repeating Characters:

    def longest_unique_substring(s):
        seen = {}
        start = max_length = 0
        for i, c in enumerate(s):
            if c in seen and seen[c] >= start:
                start = seen[c] + 1
            seen[c] = i
            max_length = max(max_length, i - start + 1)
        return max_length
   

4. Count Words or Characters:

    from collections import Counter
    def word_count(s):
        words = s.split()
        return Counter(words)
   

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4. Grammar Tips

• List Comprehensions:

  • Simplify tasks like filtering or transforming strings:

      vowels = [c for c in "hello" if c in "aeiou"]
    

• f-strings for Formatting:

  • Format strings dynamically:

      name = "Alice"
      print(f"Hello, {name}!")
    

• Set for Unique Characters:

  • Quickly identify unique characters:

      unique_chars = set("abracadabra")  # {'a', 'b', 'r', 'c', 'd'}
    

• Efficient String Iteration:

  • Use enumerate() to loop through a string with indices:

      for i, c in enumerate("hello"):
          print(i, c)