Can you use float numbers in this for loop?

Question

I need some help. I'm trying to make my for loop work with decimals, but my code won't accept floats and I'm not sure what to do next. Can anyone point out where I went wrong?

It's a code used for converting Celsius to Fahrenheit in steps (Delta) that the user defines. Here it is:

def main():

    # Handshake
    print("This program will convert a range of Celsius degrees to")
    print("Fahrenheit degrees based on your input.")

    # Ask and read low end of range
    Rangelow = eval(input("Enter the low end of your range: "))

    # Ask and read top end of range
    Rangehigh = 1 + eval(input("Enter the high end of your range: "))

    # Ask and read Delta
    Delta = eval(input("Enter the Delta for your range: "))

    #Display output
    print("Celsius to Fahrenheit by", Delta)
    for i in range(Rangelow, Rangehigh, Delta):
        print(i, "               ", 9/5 * i + 32)



main()

This is an example of what I mean:

This program will convert a range of Celsius degrees to Fahrenheit degrees based on your input. Enter the low end of your range: 3.8 Enter the high end of your range: 14.7 Enter the Delta for your range: 1.1 Celsius to Fahrenheit by 1.1 Traceback (most recent call last): File "C:\Users\jarre\Desktop\Python Programs\Conversion.py", line 27, in main() File "C:\Users\jarre\Desktop\Python Programs\Conversion.py", line 22, in main for i in range(Rangelow, Rangehigh + 1, Delta): TypeError: 'float' object cannot be interpreted as an integer

I should note that the problem seems to lie with the input, the output has no issue throwing out a decimal after the input has been converted.

Solution

You can't use the built in to do float/decimal increments but it is fairly easy to construct your own generator:

def decimal_range(start, stop, increment):
    while start < stop: # and not math.isclose(start, stop): Py>3.5
        yield start
        start += increment

for i in decimal_range(Rangelow, Rangehigh, Delta):
    ...

Or you could use numpy but this feels like a sledgehammer cracking a nut:

import numpy as np
for i in np.arange(Rangelow, Rangehigh, Delta):
    ...

Comments

[ShadowRanger]

Note: This will not behave as you expect if you use it with floats in many cases. For example, if the arguments are 0.2, 0.3, 0.1, you'll get one output (correctly excluding a "roughly 0.3" output). But if you pass it 0.7, 0.8, 0.1, you'll get two outputs, for 0.7, and 0.7999999999999.... As the name suggests, the only safe way to use this would be to convert input strings directly to decimal.Decimal, not to float.

[AChampion]

Yes, float rounding errors are a problem - so agree Decimal is the way to go. You could use math.isclose() to fix some of the errors for Py > 3.5

[Jarbcd]

How would I implement this? I'm having a hard time figuring this out

[Jarbcd]

@ShadowRanger When I use the Decimal code above, all I get is an error about three missing positions

[AChampion]

@Jarbcd You may want to ask another question because without seeing what you've done - it's hard to tell what the error is.