For loops

Introduction to Python for Developers

Jasmin Ludolf

Senior Data Science Content Developer

Individual comparisons

# Ingredient quantities
quantities = [500, 400, 15, 20, 30, 5]

# Validate values
quantities[0] < 10

False

quantities[1] < 10

False

For loop syntax

for value in sequence:
    action

for each value in sequence, perform this action
- action is indented because of the colon in the previous line
sequence = iterable e.g., list, dictionary, etc.
value = iterator, i.e., the index
- Placeholder (can give it any name), i is common

Print individual values

# Ingredients list
ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]


# Loop through and print each ingredient
for ingredient in ingredients:

    print(ingredient)

pasta
tomatoes
garlic
basil
olive oil
salt

Conditional statements in for loops

quantities = [1000, 800, 40, 30, 30, 15]

for qty in quantities:

Conditional statements in for loops

quantities = [1000, 800, 40, 30, 30, 15]

for qty in quantities:

    # Check if quantity is more than 500
    if qty > 500:
      print("Plenty in stock")
    elif qty >= 100:
        print("Enough for a small portion")
    else:
        print("Nearly out!")

Conditional statements in for loops

Plenty in stock
Enough for small
Nearly out!
Nearly out!
Nearly out!

Looping through strings

ingredient_name = "pasta"

# Loop through each character
for letter in ingredient_name:
    print(letter)

p
a
s
t
a

Useful for validating text, checking for special characters

Looping through dictionaries

ingredients = {"pasta": 500, "tomatoes": 400, "garlic": 30}


# Loop through keys and values
for item, qty in ingredients.items():
    print(item, ":", qty, "grams")

pasta : 500 grams
tomatoes : 400 grams
garlic : 30 grams

item = key (ingredient name)
qty = value (quantity)

Looping through dictionaries

ingredients = {"pasta": 500, "tomatoes": 400, "garlic": 30}
factor = 2

# Calculate scaled quantities
for item, qty in ingredients.items():
    scaled_qty = qty * factor
    print(item, ":", scaled_qty, "grams")

pasta : 1000 grams
tomatoes : 800 grams
garlic : 60 grams

Looping through dictionaries

# Loop through keys only
for item in ingredients.keys():
    print(item)

pasta
tomatoes
garlic

# Loop through values only
for qty in ingredients.values():
    print(qty, "grams")

500 grams
400 grams
30 grams

Range

range(start, end + 1)

start = starting number
end = ending number
Used to generate or modify values

for i in range(1, 6):
    print(i)

Let's practice!

Introduction to Python for Developers