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Python Control Flow

This chapter shows you some basic control flow statements in Python, including if, elif, and else statements for conditional logic, and for loops for iteration.

I will not ask you to write these, but the AI will often create them for you. I expect that you will be able to walk through the code and explain what is happening.

Outcomes:

• Explain how if, elif, and else statements control the program flow
• Walk-through boolean expressions to compare values and make decisions.
• Explain how for loops process values in arrays or lists.
• Explain how the break and continue statements control loop execution.
• Understand and use the range() function for numeric iteration.

Reading:

• Whirlwind Tour of Python Chapter 7
  • Whirlwind Tour: Control Flow

Links:

• Predict Outcomes Exercise
• Predict Outcomes Exercise Solution
• template

Example Code

If, Elif, Else Statements

x = 10
if x > 0:
    print("x is positive")
elif x == 0:
    print("x is zero")
else:
    print("x is negative")

Boolean Expressions

n = 5
print(n > 3)      # True
print(n == 5)     # True
print(n != 2)     # True

For Loops Over Lists/Arrays/Ranges

nums = [1, 2, 3, 4]
for num in nums:
    print(num)

for i in range(5):
    print(i)

For Loops to Process Numbers in Arrays/Lists

squares = []
for n in [1, 2, 3, 4]:
    squares.append(n ** 2)
print(squares)

Conditional Logic Inside Loops

nums = [1, 2, 3, 4, 5]
evens = []
for n in nums:
    if n % 2 == 0:
        evens.append(n)
print(evens)

Break and Continue

for n in range(10):
    if n == 5:
        break  # Stop the loop when n is 5
    if n % 2 == 0:
        continue  # Skip even numbers
    print(n)

Using range()

for i in range(3, 8):
    print(i)

Combining Loops and Conditionals for Data Analysis

# Print all numbers greater than 10 in a list
arr = [4, 12, 7, 15, 3]
for n in arr:
    if n > 10:
        print(n)

List comprehensions

def is_odd(n):
    return n % 2 != 0

nums = range(0, 10)
squares = [n ** 2 for n in nums]
print(squares)

odd_squares = [n ** 2 for n in nums if is_odd(n)]
print(odd_squares)

Practice Problems

• Python Practice
• Predict outcomes (word file)
  • Solution (word file)