如何字符串格式化变量?

这是我的脚本:

# I have 100 variables
x0 = 3.14
x1 = 2.72
x2 = 1.41
x3 = 2.33
.... (omit this part)
x100 = 7.77

# xi corresponds to the value that the index i of a list needs to subtract, 
# now I want to loop through the list
for i in range(100):
    list[i] -= 'x{}'.format(i)

这显然不起作用,因为变量不是字符串。那么我应该如何对变量进行字符串格式化?