Python Function inputs

Question

I am trying to teach myself Python on code academy and have written the following basic code, which is not working as whatever the input the outcome is 'Please Enter a Valid Number' and I get a message saying "Oops, try again! Make sure area_of_circle takes exactly one input (radius)."

import math
radius = raw_input("Enter the radius of your circle")
def area_of_circle(radius):
 if type(radius) == int:
 return math.pi() * radius**2
 elif type(radius) == float:
 return math.pi() * radius**2
 else:
 return "'Please enter a valid number'"
print "Your Circle area is " + area_of_circle(radius) + " units squared"

The original assignment is:

Write a function called area_of_circle that takes radius as input and returns the area of a circle. The area of a circle is equal to pi times the radius squared. (Use the math.pi in order to represent Pi.)

• Martijn Pieters: Don't use type(variablename) == sometype. At best, use isinstance(variablename, sometype). Or just don't test at all, assume it's a valid type, that's more pythonic. Catch the exception if need be, but don't test for specific types.
• Aya: Also note, math.pi is a number, not a function, so you'll need to change math.pi() to math.pi.

Answer 1

Errors in your program:

1. raw_input() returns a string, you've to convert to a float or int first.
2. Type checking is a bad idea in python
3. math.pi() is not a function just use math.pi

Use exception handling to convert the string into a number:

import math
radius = raw_input("Enter the radius of your circle: ")
def area_of_circle(radius):
 try :
 f = float(radius) #if this conversion fails then the `except` block will handle it
 return math.pi * f**2 #use just math.pi
 except ValueError:
 return "'Please enter a valid number'"
print "Your Circle area is {0} units squared".format(area_of_circle(radius))

• Henry Quekett: Thankyou I am only a day into python so still finding my legs! ;)

Answer 2

raw_input() always returns a str. You need to pass it to another type's constructor in order to convert it.

radius_val = float(radius)

Answer 3

You can type cast it while reading the input:

radius = float(raw_input("Enter the radius of your circle"))

Answer 4

Seeing as you want different paths for if the input is a int or float (which doesn't make much sense)

if type(radius) == int:
 return math.pi() * radius**2
elif type(radius) == float:

As the interpretation of raw_input()'s string could be either int or float you should evaluate it like so:

import ast
radius = ast.literl_eval(raw_input("Enter the radius of your circle"))

This way you can avoid trying to check if it is a float or int etc...

>>> type(ast.literal_eval(raw_input("Number: ")))
Number: 2.5
<type 'float'>
>>> type(ast.literal_eval(raw_input("Number: ")))
Number: 5
<type 'int'>