numbers = [0,1,2,3]

numbers[0] = input("Please enter a number")

numbers[1] = input("Please enter a second number")

numbers[2] = input("Please enter a third number")

numbers[3] = input("Please enter a fourth number")

print (numbers)

print ("Finding the Avarage")

avarage = int(numbers[0]) + int(numbers[1]) + int(numbers[2]) + int(numbers [3]) / 4

print (avarage)

而不是强制转换为float，你可以将0.0加到和:

def avg(l):
    return sum(l, 0.0) / len(l)

print reduce(lambda x, y: x + y, l)/(len(l)*1.0)

或者像之前写的那样

sum(l)/(len(l)*1.0)

1.0是为了确保你得到一个浮点除法

如果你想要的不仅仅是平均值(又名平均)，你可以看看scipy的统计:

from scipy import stats
l = [15, 18, 2, 36, 12, 78, 5, 6, 9]
print(stats.describe(l))

# DescribeResult(nobs=9, minmax=(2, 78), mean=20.11111111111111, 
# variance=572.3611111111111, skewness=1.7791785448425341, 
# kurtosis=1.9422716419666397)

l = [15, 18, 2, 36, 12, 78, 5, 6, 9]

l = map(float,l)
print '%.2f' %(sum(l)/len(l))

对于Python 3.4+，使用新的统计模块中的mean()来计算平均值:

from statistics import mean
xs = [15, 18, 2, 36, 12, 78, 5, 6, 9]
mean(xs)