I am trying to use "return" statement in Python it is not working. [closed] - return

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Closed 10 years ago.
I am trying to use the return statement. If the y is negative then program will terminate. But it is showing "ValueError: math domain error"
import math
y=-5
def df(y):
if y<=0:
print y, "is negative"
return
result = math.log(y)
print "The log of y is",result

Answer 1

I have this feeling you wanted to include your log call inside the df() function and just check it for negative first.
import math
y=-5
def df(y):
if y<=0:
print y, "is negative"
return
result = math.log(y)
return result
print "The log of y is", df(y)
To have your function return a value you have to specify what it should return. Otherwise it returns None

Answer 2

Return transfers control back to the caller. In this case, if you wanted to get the value of the function, you would need to call it, and you would need the function to actually return something. Perhaps something along these lines:
import math
def df(v):
if v <= 0:
print v, "is negative"
return
y = -5
df(y)
result = math.log(y)
print "The log of y is",result
Though I'm not really sure what you're trying to do. If you wanted your function to return something, you would use this syntax:
return [something]
... replacing [something] with the value or variable whose value you want to return. math.log returns the logarithm of its argument. You already know how to save the return value of a function:
You expect this to cause the program to exit. Returning will only exit the program if used from the main method, i.e. outside of any functions. Return gives control back to the calling routine (if there is no calling routine, the program exits). You would want to use the exit call instead:
import sys
...
sys.exit(0)
sys.exit will immediately terminate the program, passing the provided value back to the calling program. If you do not know what this is, you can use the value 0.
result = math.log(y)
As for your error message, you can't take the logarithm of a negative number, try a positive one instead. (not 0 either)
I think you want something like this:
import math
def df(v):
if v <= 0:
print v, "is negative"
return True # returns true if the value is negative or zero
return False # otherwise returns false
y = -5
if df(y): # test if negative or positive, branch on return value
return # if value was negative or zero, return (exit program)
result = math.log(y)
print "The log of y is",result

Answer 3

Your return is empty....there is no variable name or value on the same line with "return". For example, if you wanted to return the value 5, you'd put
return 5
If you wanted to return a variable foo, you'd put
return foo
Right now you are returning nothing.
Maybe you want this?
import math
y=-5
def df(y):
if y<=0:
print y, "is negative"
return "impossible to calculate"
result = math.log(y)
return result
print "The log of y is", df(y)

Answer 4

Any function needs 3 parts, as I learned for programming:
(1) input, as you "def" a function, you need to know what you want to put into the function.
For example:
def function (input1, input2):
We also called those inputs as parameters.
(2) you need to show the output:
For example, on the code you provide, if you want to return the number that variable "result" holds, you can do:
return result
or if you do not want to return, or output, anything, you can do:
return None
In python, None means nothing, at least you can think it that way for now.
(3)Function is doing things for you, so the things between
def function(inputs):
to
return None
is what you have to modify the variable from inputs into return (or output).
Hope it helps, and always work before ask any question. Good luck on Python