CODEWITHSUNDEEP
pythonfor-loop
Kalyan Kumar
Kalyan Kumar

Reputation: 407

How to change the variable in for loop?

I have this below function.

def replace_zeros(nums1):
    for n in nums1:
        print 'nums1=', nums1, 'n=', n
        if n == 0:
            nums1[nums1.index(n)] = 2
    return nums1

print replace_zeros([1,2,3,0,0,0])

which was giving me the following output

>>> print replace_zeros([1,2,3,0,0,0])
nums1= [1, 2, 3, 0, 0, 0] n= 1
nums1= [1, 2, 3, 0, 0, 0] n= 2
nums1= [1, 2, 3, 0, 0, 0] n= 3
nums1= [1, 2, 3, 0, 0, 0] n= 0
nums1= [1, 2, 3, 2, 0, 0] n= 0
nums1= [1, 2, 3, 2, 2, 0] n= 0

I am getting 'n' from nums1 only but why 'n' value is not changing even 'nums1' is changed? Could you let know how to change 'nums1' with changing value?

Consider this below python function

def replace_zeros(nums1):
    for n in nums1:
        nums1.insert(1, 2)
        nums1 = nums1[:-1]
        print 'nums1=', nums1, 'n=', n
        if n == 0:
           nums1[nums1.index(n)] = 2
return nums1

print replace_zeros([1,2,3,0,0,0])

I am getting index error at "nums1[nums1.index(n)] = 2", why still I am getting index error even if I check n==0? i.e.even though nums1 is changing inside loop, the 'n' value that we first retrieved from 'for' loop did not change. I want that 'n' to be changed along with nums1.

I am looking for something like reloading nums1 so that 'n' will change and 'n==0' condition should become False to do not enter that 'if' block so that no index error raises.

I know that what 'n' should contain will be defined when we do 'for n in nums1', but I want that 'n' to be dynamically changed with changing 'nums1' inside for loop.

Upvotes: 0

Views: 220

Answers (3)

Michael H.
Michael H.

Reputation: 3483

If you don't need the print statements, I recommend a list comprehension for the replace function:

def replace_zeros(arr):
    return [n if n != 0 else 2 for n in arr]

Upvotes: 1

michmich112
michmich112

Reputation: 774

The best method would be to use an enumeration:

def replace_zeros(nums1):
    for index,n in enumerate(nums1):
        if n == 0:
            nums1[index] = 2
        print('nums1=', nums1, 'n=', n)
    return nums1

Upvotes: 0

Sheri
Sheri

Reputation: 1413

Because you are replacing 0 with 2 but you are not changing the value of n inside if statement where you are replacing zeros 

def replace_zeros(nums1):
    for n in nums1:
        if n == 0:
            nums1[nums1.index(n)] = 2
            n = 2
        print('nums1=', nums1, 'n=', n)
    return nums1

print(replace_zeros([1,2,3,0,0,0]))

Output:

nums1= [1, 2, 3, 0, 0, 0] n= 1                                                                                        
nums1= [1, 2, 3, 0, 0, 0] n= 2                                                                                        
nums1= [1, 2, 3, 0, 0, 0] n= 3                                                                                        
nums1= [1, 2, 3, 2, 0, 0] n= 2                                                                                        
nums1= [1, 2, 3, 2, 2, 0] n= 2                                                                                        
nums1= [1, 2, 3, 2, 2, 2] n= 2                                                                                        
[1, 2, 3, 2, 2, 2]

Upvotes: 0

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