CODEWITHSUNDEEP
pythonscope
hellojinjie
hellojinjie

Reputation: 2138

Puzzled about variable scope in for-loop

This code will raise NameError: name 'i' is not defined:

for n in range(2, 101):
    for i in range(2, n):
        if n % i == 0:
            break
    if n % i != 0:
        print(n, end=' |')

This code will execute without error:

n = 97
if True:
    for i in range(2, n):
        if n % i == 0:
            break
    if n % i != 0:
        print(n, end=' |')

Could anybody tell why?

Upvotes: 1

Views: 60

Answers (2)

tripleee
tripleee

Reputation: 189910

When n is 2, range(2,n) will be an empty list, and so the body of that loop will not execute at all.

Upvotes: 4

Sayandip Dutta
Sayandip Dutta

Reputation: 15872

That has nothing to do with scopes, in fact for loops in python do not create their own scopes unless it is in a list comprehension. The reason you are getting an error is i is not getting created in the first code.

for n in range(2,101):
# at first iteration n == 2
    for i in range(2,n):
    # this is equivalent to range(2,2) in first iteration

So, there is nothing to iterate on, hence no value is assigned to i. And when it goes to n % i, it throws NameError.

In the second block:

for i in range(2, n):
# value if i is 2

As i has a value, hence defined, it does not throw NameError.

Upvotes: 3

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