Length and iteration methods in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of length and iteration over a nested list

What is the output of this Python code?

Python

nested = [[1, 2], [3, 4, 5], []]
count = 0
for sublist in nested:
    count += len(sublist)
print(count)

A TypeError

B 3

C 0

D 5

💡 Hint

Count the total number of elements inside all sublists.

The code sums the lengths of each sublist: 2 + 3 + 0 = 5.

❓ Predict Output

intermediate

Length of a dictionary after iteration

What is the output of this code snippet?

Python

d = {'a': 1, 'b': 2, 'c': 3}
for key in d:
    d[key] += 1
print(len(d))

A 3

B 6

C TypeError

D KeyError

💡 Hint

Length of a dictionary counts keys, not values.

The dictionary has 3 keys, so len(d) is 3 regardless of value changes.

❓ Predict Output

advanced

Output of iteration with modification inside loop

What is the output of this code?

Python

lst = [1, 2, 3, 4]
for i in lst:
    lst.remove(i)
print(lst)

A [1, 3]

B [2, 4]

C [3, 4]

D RuntimeError

💡 Hint

Removing items while iterating changes the list length and indices.

Removing elements while iterating skips some elements. The resulting list is [2, 4].

❓ Predict Output

advanced

Length and iteration over a generator expression

What happens when you run this code?

Python

gen = (x for x in range(5))
print(len(gen))

A 0

B 5

C TypeError

D AttributeError

💡 Hint

Generators do not support len() because they produce items on the fly.

Calling len() on a generator raises TypeError because generators have no length.

❓ Predict Output

expert

Final value after complex iteration and length checks

What is the value of variable 'result' after running this code?

Python

data = ['a', 'bb', 'ccc', 'dddd']
result = 0
for item in data:
    if len(item) % 2 == 0:
        result += len(item)
    else:
        result -= 1
print(result)

A 4

B 6

C -2

D 5

💡 Hint

Add lengths of even-length strings, subtract 1 for odd-length strings.

Lengths: 'a'(1 odd) -> -1, 'bb'(2 even) -> +2, 'ccc'(3 odd) -> -1, 'dddd'(4 even) -> +4; total = -1+2-1+4=4