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pythonrange
Luis Fernando Pineda
Luis Fernando Pineda

Reputation: 91

Python nested range function

What is the output of the following nested control structure in Python when executed?

for x in range(3):
    for y in range(x):
        print x,y

I know the answer is

1 0
2 0
2 1

But it is not clear for me why it is this output.
I know that the range(3) function would give you {0, 1, 2} so why is not the first output 0 0 instead of 1 0?

Upvotes: 2

Views: 1386

Answers (3)

fossil_fishhooks
fossil_fishhooks

Reputation: 1

Yes range(x) is [0,1,2,3,...x-1] In short, range(x) is a list of x elements starting at 0 and incrementing. As previously mentioned, this causes the first run of the second loop to never execute.

Upvotes: 0

JDurstberger
JDurstberger

Reputation: 4255

Lets go through this

First run

x = 0
range(0) is []
the print is never reached

Second Run

x = 1
range(1) is [0] <-- one element
print is called once with 1 0

Third Run

x = 2
range(2) is [0,1] <-- two elements
print is called twice with 2 0 and 2 1

Upvotes: 8

Brian
Brian

Reputation: 2242

Because range(0) returns an empty list [], so the inner loop does nothing the first time it is run.

Upvotes: 8

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