How to add a condition in Python for loop

Question

In Java, the FOR loop syntax offers a place where we can add a condition. For instance, in the below code the condition is i*j < n

for (i=0; i*j < n; i++) 
{ ... }

In Python, how can we add such condition in the for loop statement?

for i in range(n):

I know that we can add an if statement inside the for loop, but I am concerned that it will increase the run time to O(n). Please advice.

I dont think you will have any diff in O(n) in any case. Instead of `for`, you can use `while` too — Gurupad Hegde, Aug 25 '16 at 18:37
As far as the example goes, you could achieve the same thing with `for i in range(n//j+1)`. — fuglede, Aug 25 '16 at 18:42

score 4 · Accepted Answer · answered Aug 25 '16 at 18:37

4

the for has a complexity of O(n), so a if does not change the complexity.

The for(i=0; i*j < n; i++) in Java is represented by while in Python:

i = 0  # initialization
while i * j < n:  # conditions
   do_something
   i += 1  # step

answered Aug 25 '16 at 18:37

Daniel

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score 1 · Answer 2 · answered Aug 25 '16 at 18:38

When I switched from C to python, this was one of my biggest worries, but it turns out that it is actually a misunderstanding of of syntax. In python, although you can write for i in range(n) it is usually a sign that you are doing something else wrong. It is considered better to loop through elements rather than numbers. For a concrete example, in C, you might write

for(i=0; i<len(str); i++){
    str[i] blah blah blah
}

In python the way you would probably do this is to iterate through the characters directly:

for char in str:
    char blah blah blah

How to add a condition in Python for loop

2 Answers2