Control Flow

if x > 0:
    print("positive")
elif x == 0:
    print("zero")
else:
    print("negative")

# One-liner (ternary / conditional expression)
value = "yes" if condition else "no"

# Nested ternary (readable only when very simple)
label = "high" if x > 100 else "mid" if x > 50 else "low"

for item in [1, 2, 3]:
    print(item)

# String characters
for ch in "hello":
    print(ch)

# Range
for i in range(5):          # 0 1 2 3 4
    pass
for i in range(2, 8):       # 2 3 4 5 6 7
    pass
for i in range(0, 10, 2):   # 0 2 4 6 8
    pass
for i in range(10, 0, -1):  # 10 9 8 ... 1  (countdown)
    pass

# Enumerate — index + value
for i, val in enumerate(lst):
    print(i, val)
for i, val in enumerate(lst, start=1):  # 1-based index
    print(i, val)

# Zip — parallel iteration
for a, b in zip(list1, list2):
    pass
for a, b, c in zip(l1, l2, l3):
    pass

# zip stops at shortest; use zip_longest for full coverage:
from itertools import zip_longest
for a, b in zip_longest(l1, l2, fillvalue=0):
    pass

# Unpack tuples
pairs = [(1, "a"), (2, "b")]
for num, letter in pairs:
    print(num, letter)

# Dict iteration
for key in d:                  # keys (default)
    pass
for val in d.values():         # values
    pass
for key, val in d.items():     # key-value pairs
    pass

while condition:
    do_something()

# Infinite loop with break
while True:
    data = get_data()
    if not data:
        break
    process(data)

# Common pattern: index-based
i = 0
while i < len(lst):
    print(lst[i])
    i += 1

for i in range(10):
    if i == 3:
        continue    # skip to next iteration
    if i == 7:
        break       # exit loop immediately
    print(i)

# pass — syntactic no-op placeholder
if condition:
    pass            # do nothing (keeps block valid)

class Empty:
    pass

def stub():
    pass

for item in collection:
    if item == target:
        print("found")
        break
else:
    print("not found")  # runs only if loop exhausted without break

# Same for while
while queue:
    item = queue.pop()
    if done(item):
        break
else:
    print("queue exhausted")

match command:
    case "quit":
        quit()
    case "go" | "move":
        move()
    case _:            # wildcard / default
        print("unknown")

# Match with capture
match point:
    case (0, 0):
        print("origin")
    case (x, 0):
        print(f"x-axis at {x}")
    case (0, y):
        print(f"y-axis at {y}")
    case (x, y):
        print(f"point at {x}, {y}")

# Match dataclass / object attributes
from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

match shape:
    case Point(x=0, y=0):
        print("origin")
    case Point(x=x, y=y):
        print(f"{x}, {y}")

# Guards (if clause inside case)
match value:
    case n if n < 0:
        print("negative")
    case n if n == 0:
        print("zero")
    case n:
        print("positive")

# Sequence patterns
match lst:
    case []:
        print("empty")
    case [x]:
        print(f"single: {x}")
    case [first, *rest]:
        print(f"head={first}, tail={rest}")

# Mapping patterns
match d:
    case {"action": "buy", "item": item}:
        buy(item)
    case {"action": "sell", "item": item}:
        sell(item)

try:
    result = 10 / x
except ZeroDivisionError:
    result = 0
except (TypeError, ValueError) as e:
    print(f"error: {e}")
    result = None
except Exception as e:
    raise  # re-raise
else:
    print("no exception occurred")   # runs only if no exception
finally:
    cleanup()                         # always runs

with open("file.txt") as f:
    data = f.read()

# Multiple context managers
with open("in.txt") as fin, open("out.txt", "w") as fout:
    fout.write(fin.read())

# Parenthesized (Python 3.10+)
with (
    open("in.txt") as fin,
    open("out.txt", "w") as fout,
):
    fout.write(fin.read())

from itertools import islice, takewhile, dropwhile, chain

# Take first n items from any iterable
list(islice(iterable, 5))

# Take items while condition holds
list(takewhile(lambda x: x < 5, [1, 3, 5, 7]))  # [1, 3]

# Drop items while condition holds, then yield rest
list(dropwhile(lambda x: x < 5, [1, 3, 5, 7]))  # [5, 7]

# Chain multiple iterables
for item in chain([1, 2], [3, 4], [5]):
    print(item)

# Filter equivalent
evens = [x for x in range(20) if x % 2 == 0]

# any / all — short-circuit over iterables
any(x > 0 for x in lst)   # True if at least one positive
all(x > 0 for x in lst)   # True if all positive

# next with default — first match
first = next((x for x in lst if x > 5), None)