Flujo de control - Tutorial Python | TechLead

Sentencias condicionales

Python usa if, elif y else para la ramificacion condicional. A diferencia de muchos lenguajes, Python no tiene una sentencia switch/case en versiones anteriores, pero Python 3.10 introdujo el pattern matching estructural con match/case.

# Basic if/elif/else
temperature = 35

if temperature > 30:
    print("It's hot outside!")
elif temperature > 20:
    print("Nice weather!")
elif temperature > 10:
    print("A bit chilly")
else:
    print("It's cold!")

# Conditional expressions (ternary operator)
age = 20
status = "adult" if age >= 18 else "minor"
print(status)  # "adult"

# Chained comparisons (Pythonic!)
x = 15
if 10 < x < 20:
    print("x is between 10 and 20")

# Multiple conditions
score = 85
has_bonus = True

if score >= 80 and has_bonus:
    print("You passed with distinction!")

# Truthy/falsy in conditions
items = [1, 2, 3]
if items:  # Non-empty list is truthy
    print(f"List has {len(items)} items")

name = ""
if not name:  # Empty string is falsy
    print("Name is empty")

Bucles for

El bucle for de Python itera sobre cualquier objeto iterable — listas, cadenas, tuplas, diccionarios, rangos, archivos y mas. Es fundamentalmente diferente de los bucles for de estilo C; piensa en el como un bucle "para cada".

# Iterating over a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# range() for numeric iteration
for i in range(5):         # 0, 1, 2, 3, 4
    print(i)

for i in range(2, 10, 3):  # 2, 5, 8 (start, stop, step)
    print(i)

# enumerate() - get index and value
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# Iterating over a dictionary
scores = {"Alice": 95, "Bob": 87, "Charlie": 92}
for name, score in scores.items():
    print(f"{name}: {score}")

for key in scores:           # iterates over keys by default
    print(key)

for value in scores.values():  # iterate over values
    print(value)

# zip() - iterate over multiple iterables in parallel
names = ["Alice", "Bob", "Charlie"]
ages = [30, 25, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age}")

# Nested loops
for i in range(3):
    for j in range(3):
        print(f"({i}, {j})", end=" ")
    print()

Bucles while

El bucle while se repite mientras una condicion sea verdadera. Usalo cuando no sabes de antemano cuantas iteraciones necesitas. Siempre asegurate de que haya una forma de que la condicion se vuelva falsa, de lo contrario crearas un bucle infinito.

# Basic while loop
count = 0
while count < 5:
    print(count)
    count += 1

# While with user input
# while True:
#     user_input = input("Enter 'quit' to exit: ")
#     if user_input == "quit":
#         break
#     print(f"You entered: {user_input}")

# While with else (executes if loop completes without break)
n = 10
while n > 0:
    n -= 1
    if n == 5:
        continue  # skip 5
    print(n)
else:
    print("Loop completed normally")

# Practical example: binary search
def binary_search(arr, target):
    low, high = 0, len(arr) - 1
    while low <= high:
        mid = (low + high) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            low = mid + 1
        else:
            high = mid - 1
    return -1

sorted_list = [1, 3, 5, 7, 9, 11, 13]
print(binary_search(sorted_list, 7))  # 3

Break, Continue y Else

break sale del bucle actual completamente. continue salta el resto de la iteracion actual y pasa a la siguiente. Python soporta de forma unica una clausula else en los bucles, que se ejecuta solo si el bucle termina sin encontrar un break.

# break - exit the loop
for n in range(100):
    if n > 5:
        break
    print(n)  # 0, 1, 2, 3, 4, 5

# continue - skip current iteration
for n in range(10):
    if n % 2 == 0:
        continue
    print(n)  # 1, 3, 5, 7, 9

# for/else - else runs only if no break occurred
def find_prime_factor(n):
    for i in range(2, n):
        if n % i == 0:
            print(f"First factor of {n} is {i}")
            break
    else:
        print(f"{n} is prime!")

find_prime_factor(17)  # "17 is prime!"
find_prime_factor(15)  # "First factor of 15 is 3"

Pattern Matching estructural (Python 3.10+)

Python 3.10 introdujo las sentencias match/case, que son mucho mas poderosas que un simple switch/case. Soportan desestructuracion, guardas, coincidencia de tipos y patrones complejos.

# Basic pattern matching
def handle_command(command):
    match command.split():
        case ["quit"]:
            print("Quitting...")
        case ["go", direction]:
            print(f"Going {direction}")
        case ["get", item] if item != "sword":
            print(f"Picking up {item}")
        case ["get", "sword"]:
            print("The sword is too heavy!")
        case _:
            print(f"Unknown command: {command}")

handle_command("go north")    # Going north
handle_command("get shield")  # Picking up shield
handle_command("get sword")   # The sword is too heavy!

# Pattern matching with types
def process_value(value):
    match value:
        case int(n) if n > 0:
            print(f"Positive integer: {n}")
        case int(n):
            print(f"Non-positive integer: {n}")
        case str(s):
            print(f"String: {s}")
        case [x, y]:
            print(f"Two-element list: {x}, {y}")
        case {"name": name, "age": age}:
            print(f"Person: {name}, age {age}")
        case _:
            print("Something else")

process_value(42)                          # Positive integer: 42
process_value("hello")                     # String: hello
process_value([1, 2])                      # Two-element list: 1, 2
process_value({"name": "Alice", "age": 30})  # Person: Alice, age 30

Puntos clave

Comparaciones encadenadas: Usa 10 < x < 20 en lugar de x > 10 and x < 20
for/else: El bloque else se ejecuta cuando el bucle termina sin break
Prefiere for sobre while: Usa bucles for cuando iteras sobre secuencias
Pattern matching: Usa match/case para logica condicional compleja en Python 3.10+