问题
I'm learning Python now, yay! Anyway, I have small problem. I don't see problem in here:
x = 3
y = 7
z = 2
print "I told to the Python, that the first variable is %d!" % x
print "Anyway, 2nd and 3rd variables sum is %d. :)" % y + z
But Python thinks different - TypeError: cannot concatenate 'str' and 'int' objects.
Why is that so? I haven't setted any variable as string... as much as I see.
回答1:
% has a higher precedence than +, so s % y + z is parsed as (s % y) + z.
If s is a string, then s % x is a string, and (s % y) + z attempts to add a string (the result of s % y) and an integer (the value of z).
回答2:
You need to put parenthesis: (y+z)
来源：https://stackoverflow.com/questions/7001664/typeerror-cannot-concatenate-str-and-int-objects