Average Function

This is the shortest question in the Python (Basic) pool. It checks one thing: do you know how to write a function that takes any number of arguments.

What the question asks

You write a function called avg. HackerRank reads a line of space-separated integers, unpacks them into your function as separate arguments, and prints whatever you return with two decimal places. Your function has to return the arithmetic mean of all the numbers it receives. Sometimes it gets two numbers, sometimes ten.

Function to write

def avg(*nums):
    ...

The editor only says “write your code here”. There is no ready-made signature, so you have to type the whole def line yourself. The name must be exactly avg, because the hidden code calls avg(*nums).

Solution

def avg(*nums):
    return sum(nums) / len(nums)

That is all you write. The input reading and the '%.2f' printing are already in HackerRank’s code below yours.

How it works

• *nums collects every positional argument into a tuple. If the caller writes avg(1, 2, 3), then nums is (1, 2, 3).
• sum(nums) adds them up and len(nums) counts them.
• In Python 3, / always gives a float, so avg(2, 5) returns 3.5 and not 3.
• The stub formats the result with '%.2f', so 1.3333… is printed as 1.33. You do not need to round anything.

Mistakes that fail the hidden tests

• Taking a list instead of *nums. def avg(nums) breaks as soon as the stub calls avg(*nums) with more than one number: you get a TypeError about too many positional arguments.
• Using //. Floor division turns 2.5 into 2, and the output becomes 2.00 instead of 2.50.
• Rounding yourself. round(x, 2) before returning is harmless most of the time, but returning a formatted string like f"{x:.2f}" fails, because '%.2f' % "2.50" raises a TypeError.
• Printing instead of returning. The stub writes your return value to the output file. If you print and return nothing, the stub tries to format None and crashes.
• Wrong function name. average or Avg gives a NameError.

Try it on sample data

Input line 1 2 3 4, which the stub passes as avg(1, 2, 3, 4):

print(avg(1, 2, 3, 4))
print('%.2f' % avg(1, 2, 3, 4))
print('%.2f' % avg(1, 1, 2))

Output from my run:

2.5
2.50
1.33