For loops

Introduction to Python for Developers

George Boorman

Curriculum Manager, DataCamp

Individual comparisons

# Prices list
prices = [9.99, 8.99, 35.25, 1.50, 5.75]

prices[0] > 10

False

prices[0] < 5

False

prices[0] >= 5 and prices[0] <= 10

True

For loop syntax

for value in sequence:
    action

for each value in sequence, perform 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

# Prices list
prices = [9.99, 8.99, 35.25, 1.50, 5.75]


# Print each value in prices
for price in prices:

    print(price)

9.99
8.99
35.25
1.5
5.75

Conditional statements in for loops

for price in prices:

Conditional statements in for loops

for price in prices:

    # Check if the price is more than 10
    if price > 10:

Conditional statements in for loops

for price in prices:

    # Check if the price is more than 10
    if price > 10:
        print("More than $10")

Conditional statements in for loops

for price in prices:

    # Check if the price is more than 10
    if price > 10:
        print("More than $10")
    # Check if the price is less than 5
    elif price < 5:
        print("Less than $5")

Conditional statements in for loops

for price in prices:

    # Check if the price is more than 10
    if price > 10:
        print("More than $10")
    # Check if the price is less than 5
    elif price < 5:
        print("Less than $5")
    # Otherwise print the price
    else:
        print(price)

Conditional statements in for loops

9.99
8.99
More than $10
Less than $5
5.75

Looping through strings

username = "george_dc"

# Loop through username and print each character
for char in username:
    print(char)

g
e
o
r
g
e
_
d
c

Looping through dictionaries

products_dict = {"AG32":87.99, "HT91":21.50,
                 "PL65":43.75, "OS31":19.99,
                 "KB07":62.95, "TR48":98.0}


# Loop through keys and values
for key, val in products_dict.items():
    print(key, val)

AG32 87.99
HT91 21.5
PL65 43.75
OS31 19.99
KB07 62.95
TR48 98.0

Looping through dictionaries

# Loop through keys
for key in products_dict.keys():
    print(key)

AG32
HT91
PL65
OS31
KB07
TR48

# Loop through values
for val in products_dict.values():
    print(val)

Range

Can use for loops to update variables

range(start, end + 1)

start = inclusive
end = not inclusive

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

Building a counter

# No visits yet
visits = 0

# Loop through numbers 1-10
for i in range(1, 11):

    # Add one to visits during each iteration
    visits += 1 # Same as visits = visits + 1


print(visits)

Let's practice!

Introduction to Python for Developers