why round() builtin function in python3 is not working for me?

Question

for a given student we need to calculate average marks. Input will be like this:

3

Krishna 67 68 69

Arjun 70 98 63

Malika 52 56 60

Malika

code:

if __name__ == '__main__':
n = int(input()) # takes input
student_marks = {} 
for _ in range(n):
    name, *line = input().split()
    scores = list(map(float, line))
    student_marks[name] = scores
query_name = input()

a,b,c=student_marks[query_name]
avg=(a+b+c)/3   #avg is calculated.
output =round(avg,2) ## why can't I use print(round(avg,2)) to give 56.00 but it is giving 56.0 only
print("%.2f" % output) # for my output in two decimal places I had to use this

Answer 1

In order to get what you expected ,use format function instead of round function.

>>> num=3.65
>>> "The number is {:.2f}".format(num)
'The number is 3.65'

or equivalently with f-strings (Python 3.6+):

>>> num = 3.65
>>> f"The number is {num:.2f}"
'The number is 3.65'

As always, the float value is an approximation:

>>> "{}".format(f)
'3.65'
>>> "{:.10f}".format(f)
'3.6500000000'
>>> "{:.20f}".format(f)
'3.64999999999999991118'

For 56

>>> num=56
>>> "The number is {:.2f}".format(num)
'The number is 56.00'