u2-script-loops-conditions

Question 1

What’s the difference between range(3, 20) and range(3, 20, 3)?

Answer 1

range(3, 20) generates numbers 3 through 19 incrementing by 1, while range(3, 20, 3) generates only numbers divisible by 3: 3, 6, 9, 12, 15, 18

Question 2

How can you check if a number is divisible by 3 in Python?

Answer 2

Use the modulo operator: if number % 3 == 0. If the remainder is 0, the number is divisible by 3.

Question 3

What are two ways to exit a while loop in Python?

Answer 3

1) Using a break statement to exit immediately, or
2) Using a condition in the while statement that becomes False when you want to exit

Question 4

What’s the difference between these two loops: ‘while True:’ and ‘while condition:’?

Answer 4

‘while True:’ creates an infinite loop that must be exited with ‘break’, while ‘while condition:’ automatically exits when the condition becomes False

Question 5

How do you check if a character is a digit in Python?

Answer 5

Use the string method isdigit(). Example: char.isdigit() returns True if char is a digit (0-9)

Question 6

How do you check if a character is lowercase in Python?

Answer 6

Use the string method islower(). Example: char.islower() returns True if char is a lowercase letter

Question 7

What does enumerate() do in a for loop?

Answer 7

enumerate() provides both the index and value in each iteration. Example:

for i, char in enumerate("hello")

gives (0, ‘h’), (1, ‘e’), etc.

Question 8

What is the ‘else’ clause in a while loop used for?

Answer 8

The else clause in a while loop executes when the loop completes normally (not through a break statement). Example from password checker:

while try_count < try_limit:
    if password == secret_pwd:
        break
    else:
        print("Contact administrator")

Question 9

How can you create a counter-controlled loop in Python?

Answer 9

Two ways:
1) Using a for loop with range:

for i in range(limit)

or

2) Using a while loop with a counter:

count = 0
while count < limit:
    count += 1```

Question 10

What’s the difference between += and = when working with strings?

Answer 10

’+=’ appends to the existing string, while ‘=’ creates a new string assignment. Example:

s += "new"  # Appends "new" to existing string
s = "new"   # Replaces entire string with "new"```

Question 11

How can you nest loops to compare characters between two strings?

Answer 11

Use a nested for loop structure:

for i, char1 in enumerate(string1):
    for char2 in string2:
        if char1 == char2:
            # do something```

Question 12

What’s the purpose of assert statements in Python code?

Answer 12

assert statements help verify that conditions are met and catch logical errors. Example:

assert len(s) == n_digits + n_lowercase + n_other

verifies that all characters were counted correctly

Question 13

How can you accumulate values in a loop?

Answer 13

Use a variable initialized before the loop and update it inside the loop:

result = 0
for value in range(3, 20):
    result += value ** 2```