TypeError: cannot concatenate 'str' and 'int' objects

Question

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.

Solution 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).

Solution 2

You need to put parenthesis: (y+z)

Comments

[carlosdc]

If not python thinks you're doing ("Anyway %d" % y)+z

[Dan D.]

% has lower precedence than +, so a % b + c is parsed as (a % b) + c, while what you want is a % (b + c)

[nagisa]

Because it formats string with y ant then tries to concatenate formatted string with z, which yields error, because they are of different types.

[MaddTheSane]

Grammar reference: docs.python.org/reference/…

[daGrevis]

Thanks for answers, guys! I just smell that learning Python will be so much fun for me! :))