1. Grammar Tips

1.1. List Comprehensions:

• Simplify tasks like filtering or transforming strings:

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

1.2. Efficient String Iteration:

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

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

1.3. Set for Unique Characters:

• Quickly identify unique characters:

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

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2. String Methods (Built-in Functions)

2.1. Basic Operations

• len(s): Get the length of a string.

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

2.2. 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.

2.3. 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.

2.4. 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.

2.5. 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.

2.6. Slicing and Reversing

• s[start:end:step]: Slice a string.

• s[::-1]: Reverse a string.

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3. Libraries for String Manipulation

3.1. 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']
    

3.2. collections

• collections.Counter:

  • Count the frequency of characters or substrings.

  • Example:

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