String Operations

Whitespace Removal

text = '\n   x  yz    \n'
print(text.strip())   # Removes leading and trailing whitespace and newlines
print(text.rstrip())  # Removes trailing whitespace only
print(text.lstrip())  # Removes leading whitespace only

Substitution

print(text.replace('x', 'X'))  # Replaces all 'x' characters with 'X'
print(text.replace(' ', ''))   # Removes all spaces by replacing them with empty strings

Locating Substrings

sample = 'hello world'
print(sample.find('o'))       # Returns -1 if not found
print(sample.index('o'))      # Raises ValueError if not found

Prefix and Suffix Checks

filename = 'document.jpg'
print(filename.startswith('doc'))   # Checks if string starts with 'doc'
print(filename.endswith('.jpg'))    # Checks if string ends with '.jpg'

Counting and Length

phrase = 'character count'
print(phrase.count('c'))      # Counts occurrences of 'c'
print(len(phrase))           # Returns total length

Padding and Alignment

print(phrase.center(30, '-'))  # Centers string within 30 characters using '-' for padding
print('42'.zfill(5))          # Pads with leading zeros to reach length 5

Case Conversion

mixed = 'PyThOn'
print(mixed.upper())        # Converts to uppercase
print(mixed.lower())        # Converts to lowercase
print(mixed.capitalize())   # Capitalizes first character
print(mixed.title())        # Capitalizes first character of each word

String Type Validation

test1 = 'ABC!123'
test2 = '测试文字'
test3 = '¾123'

print(test1.isupper())      # Checks if all alphabetic characters are uppercase
print(test1.islower())      # Checks if all alphabetic characters are lowercase
print(test2.isalpha())      # Checks if string contains only letters or characters
print(test2.isalnum())      # Checks if string contains only alphanumeric characters
print(test1.isascii())      # Checks if string contains only ASCII characters

print(test3.isdecimal())    # Checks for decimal digits only (0-9)
print(test3.isdigit())      # Checks for digit characters including superscripts
print(test3.isnumeric())    # Checks for numeric characters including fractions

Spiltting and Joining

# Splitting
names = 'alice,bob,charlie,david'
print(names.split(','))     # Splits by comma into list

# Joining
name_list = ['alice', 'bob', 'charlie', 'david']
print('-'.join(name_list))  # Joins list elements with hyphen

String Formatting

# format() method
template = 'User {} logged in at {}'
print(template.format('admin', '14:30'))

# format() with named parameters
query = 'INSERT INTO users(id, name, email) VALUES({id}, {name}, {email})'
print(query.format(id=1, name='john', email='john@example.com'))

# format_map() with dictionary
data = {'id': 2, 'name': 'jane', 'email': 'jane@example.com'}
print(query.format_map(data))

List Operations

Adding Elements

fruits = ['apple', 'banana']
fruits.append('cherry')           # Adds to end
fruits.insert(1, 'blueberry')     # Inserts at index 1
more_fruits = ['date', 'elderberry']
fruits.extend(more_fruits)        # Extends with another list

Accessing Elements

items = [10, 20, 30, 40, 50]
print(items[0])                   # First element
print(items[-1])                  # Last element
print(items[1:4])                 # Slice from index 1 to 3
print(items[::2])                 # Every second element

Element Information

values = [5, 2, 8, 2, 9, 2]
print(values.count(2))            # Count occurrences of 2
print(len(values))                # Total number of elements
print(values.index(8))            # First index of 8

Modifying Elements

numbers = [1, 2, 3, 4, 5]
numbers[2] = 99                   # Modify single element
numbers[1:3] = [88, 77]           # Modify slice
numbers[3:] = [66, 55, 44]        # Replace from index 3 onward

Sorting

data = [3, 1, 4, 1, 5, 9]
data.reverse()                    # Reverse in place
data.sort()                       # Sort ascending
data.sort(reverse=True)           # Sort descending

Removing Elements

items = ['a', 'b', 'c', 'd', 'e']
items.remove('c')                 # Remove first 'c'
removed = items.pop(1)            # Remove and return element at index 1
last = items.pop()                # Remove and return last element
del items[0]                      # Delete element at index 0

Tuple Operations

Tuples are immutable sequences with limited methods:

# Creation and access
config = ('localhost', 'admin', 'secret', 5432)
print(config[0])                  # Access by index
print(config[1:3])                # Slicing

# Tuple operations
t1 = (1, 2, 3)
t2 = (4, 5, 6)
combined = t1 + t2                # Concatenation
x, y, z = t1                      # Unpacking

# Available methods
print(t2.count(5))                # Count occurrences
print(t2.index(6))                # Find first index

Dictionary Operations

Creation

# Multiple creation methods
user1 = {'name': 'Alice', 'age': 30}
user2 = dict(name='Bob', age=25)
user3 = dict([('name', 'Charlie'), ('age', 35)])

Access and Modification

person = {'name': 'David', 'city': 'London'}
print(person['name'])             # Access by key
person['age'] = 28                # Add new key-value pair
person['city'] = 'Paris'          # Modify existing value

# Safe access
print(person.get('email', 'N/A')) # Returns 'N/A' if key doesn't exist

# Key operations
print('name' in person)           # Check key existence
print(person.keys())              # View all keys
print(person.values())            # View all values
print(person.items())             # View all key-value pairs

Updates and Merging

original = {'a': 1, 'b': 2}
updates = {'b': 3, 'c': 4}
original.update(updates)          # Merge dictionaries

Removal

data = {'x': 10, 'y': 20, 'z': 30}
removed = data.pop('y')           # Remove and return value for 'y'
last = data.popitem()             # Remove and return last inserted item
del data['x']                     # Delete specific key

Set Operations

Sets store unique, unordered elements:

# Creation
unique_numbers = {1, 2, 3, 4, 5}
another_set = set([3, 4, 5, 6, 7])

# Basic operations
unique_numbers.add(6)             # Add single element
unique_numbers.update([7, 8, 9])  # Add multiple elements
unique_numbers.remove(3)          # Remove element (raises error if missing)
unique_numbers.discard(10)        # Remove element (no error if missing)
popped = unique_numbers.pop()     # Remove and return arbitrary element

# Set operations
print(unique_numbers.union(another_set))        # All elements from both sets
print(unique_numbers.intersection(another_set)) # Common elements
print(unique_numbers.difference(another_set))   # Elements in first not in second
print(unique_numbers.symmetric_difference(another_set)) # Elements in either but not both

# Comparisons
print({1, 2}.issubset({1, 2, 3}))    # Check if first is subset of second
print({1, 2, 3}.issuperset({1, 2}))  # Check if first is superset of second
print({1, 2}.isdisjoint({3, 4}))     # Check if sets have no common elements