What is a Python list and what operations are most commonly used?

A list is Python's built-in ordered, mutable sequence. It can hold items of any type — including other lists — and grows or shrinks dynamically. Lists are backed by a C array that doubles in capacity when it runs out of space, so appending is O(1) amortised.

# Creation
items = [10, 'hello', 3.14, True]

# Indexing (zero-based, negative counts from end)
print(items[0])   # 10
print(items[-1])  # True

# Slicing [start:stop:step]
print(items[1:3]) # ['hello', 3.14]

# Mutating
items.append('new')    # add to end
items.insert(1, 99)    # insert at index 1
items.remove('hello')  # remove first occurrence
popped = items.pop()   # remove and return last element
items.sort()           # in-place sort (only works if items are comparable)
items.reverse()        # in-place reverse

# Length and membership
print(len(items))        # number of elements
print('new' in items)    # True / False

List comprehension is the idiomatic way to build a new list from an existing iterable:

squares = [x**2 for x in range(1, 6)]  # [1, 4, 9, 16, 25]
evens   = [x for x in range(10) if x % 2 == 0]  # [0, 2, 4, 6, 8]

Lists are passed by reference — assigning a list to a second variable gives you a second name for the same object. Use list.copy() or list[:] for a shallow copy, or copy.deepcopy() when the list contains nested mutable objects.

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