"TypeError: cannot concatenate 'str' and 'int' objects" when trying to use printf-style formatting

I don't see problem in here, but Python thinks different:

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

I get TypeError: cannot concatenate 'str' and 'int' objects.

Why is that so? I haven't setted an开发者_Go百科y variable as string... as much as I see.

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% 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).

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You need to put parenthesis: (y+z)