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I'm a noobie, learning to code and i stumbled upon an incorrect output while practicing a code in python, please help me with this. I tried my best to find the problem in the code but i could not find it.

Code:

def compare(x,y):
    if x>y:
        return 1
    elif x==y:
        return 0
    else:
        return -1

i=raw_input("enter x\n")
j=raw_input("enter y\n")

print compare(i,j)

Output:

-> python python.py
enter x
10
enter y
5
-1

The output that i had to receive is 1 but the output that i receive is -1. Please help me with the unseen error in my code.

Thank you.

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3 Answers 3

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1

raw_input returns a string always.

so you have to convert the input values into numbers.

i=raw_input("enter x\n")
j=raw_input("enter y\n")
print compare(i,j)

should be 

i=int(raw_input("enter x\n"))
j=int(raw_input("enter y\n"))
print compare(i,j)
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2 Comments

now i understand that raw_input returns string value if my code is as follows: def compare(x,y): if x>y: return 1 elif y>x: return -1 else: return 0 i=raw_input("enter x\n") j=raw_input("enter y\n") print compare(i,j) then the output that i recieve is: -> python python.py enter x 10 enter y 5 -1 how come the output is -1 rather than 0
you can compare alphabets also, they are ordered as per their ascii value you can check in the repl by typing 'b' < 'a' which should give you False and 'a' < 'b' will give you True. That is why you were not getting 0
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Your issue is that raw_input() returns a string, not an integer.

Therefore, what your function is actually doing is checking "10" > "5", which is False, therefore it falls through your if block and reaches the else clause.

To fix this, you'll need to cast your input strings to integers by wrapping the values in int().

i.e.

i = int(raw_input("enter x\n")).

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1 Comment

Actually there's nothing like "casting" in Python. "casting" (in "type casting") means "interpreting the same variable as being of another type", which is not possible in Python. What int(somestr) does is instanciating a new int object from the numeric value of somestr, so the correct term would be "converting", not "casting".
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Use the inbuilt cmp builtin function.

>>> help(cmp)
Help on built-in function cmp in module __builtin__:

cmp(...)
    cmp(x, y) -> integer

    Return negative if x<y, zero if x==y, positive if x>y.

So your function will look like this.

>>> def compare(x,y):
...   return  cmp(x,y)
...
>>>

Then get two variables using raw_input() which returns string, So If you are typing two numbers with a blankspace in the middle, splitting based on blank space will save two numbers in these x and y, and then apply map function which takes two parameters, one int function and the sequence which is nothing but a list created out of split(). 

>>> x,y = map(int, raw_input().split())
3 2

Now Comparing the x and y, Since x = 3 and y =2, Now since as per the documentation of cmp(), It Return negative if xy.

>>> compare(x,y)
1
>>> compare(y,x)
-1
>>> compare(x-1,y)
0
>>>
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2 Comments

Don't post screen captures as answers please - and posting code without explanations does not make for a good answer.
@bruno desthuilliers: Updated my answer with detail description.

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