Simultaneous Assign¶

Basic Unpacking¶

1. Simple Case¶

a, b = 1, 2
print(f"{a = }, {b = }")  # a = 1, b = 2

Process: 1. Right side: Create tuple (1, 2) 2. Left side: Unpack to a and b

2. Tuple Creation¶

# Tuple is created
x = 1, 2
print(type(x))  # <class 'tuple'>

# Internally
a, b = 1, 2
# (1, 2) created, then unpacked

Advanced Unpacking¶

1. Starred Expression¶

numbers = list(range(10))
first, *middle, last = numbers

print(f"{first = }")   # first = 0
print(f"{middle = }")  # middle = [1,2,...,8]
print(f"{last = }")    # last = 9

2. Position Matters¶

*start, last = [1, 2, 3, 4]
print(f"{start = }")  # start = [1, 2, 3]
print(f"{last = }")   # last = 4

first, *end = [1, 2, 3, 4]
print(f"{first = }")  # first = 1
print(f"{end = }")    # end = [2, 3, 4]

Throwaway Variables¶

1. Underscore¶

# Ignoring values
_, status_code, _ = ("HTTP", 200, "OK")
print(f"Status: {status_code}")

2. With Star¶

first, *_, last = range(10)
print(f"{first = }")  # first = 0
print(f"{last = }")   # last = 9

Swapping Pattern¶

1. Elegant Swap¶

a, b = 10, 20
print(f"Before: {a = }, {b = }")

a, b = b, a
print(f"After: {a = }, {b = }")
# Before: a = 10, b = 20
# After: a = 20, b = 10

2. How It Works¶

# Internally:
# 1. Create tuple (b, a) = (20, 10)
# 2. Unpack to a, b
# No temp variable needed!

3. Multiple Swap¶

a, b, c = 1, 2, 3
a, b, c = c, a, b
print(f"{a = }, {b = }, {c = }")
# a = 3, b = 1, c = 2

Function Returns¶

1. Multiple Returns¶

def get_coordinates():
    return 10, 20, 30

x, y, z = get_coordinates()
print(f"{x = }, {y = }, {z = }")

2. Partial Unpacking¶

def get_data():
    return "name", 25, "city"

name, *rest = get_data()
print(f"{name = }")  # name = 'name'
print(f"{rest = }")  # rest = [25, 'city']

Nested Unpacking¶

1. Nested Tuples¶

data = (1, (2, 3), 4)
a, (b, c), d = data
print(f"{a = }, {b = }, {c = }, {d = }")
# a = 1, b = 2, c = 3, d = 4

Iteration Patterns¶

1. Enumerate¶

items = ['a', 'b', 'c']
for i, item in enumerate(items):
    print(f"{i}: {item}")
# 0: a
# 1: b
# 2: c

2. Dictionary Items¶

data = {'x': 10, 'y': 20}
for key, value in data.items():
    print(f"{key} = {value}")

3. Zip¶

names = ['Alice', 'Bob']
ages = [25, 30]

for name, age in zip(names, ages):
    print(f"{name} is {age}")

Common Mistakes¶

1. Length Mismatch¶

# Too many values
try:
    a, b = 1, 2, 3
except ValueError as e:
    print(e)  # too many values

# Too few values
try:
    a, b, c = 1, 2
except ValueError as e:
    print(e)  # not enough values

2. Star Required¶

# This fails
# a, b = [1, 2, 3, 4, 5]
# ValueError

# This works
a, *b = [1, 2, 3, 4, 5]
print(f"{a = }, {b = }")
# a = 1, b = [2, 3, 4, 5]