TypeError: need a summation variable

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I am writing a sage script (IDE is PyCharm using the sage python interpreter):

from sage.all import *
k = var('k')
symbolic_sum(k,k,0,10)

When I run this, I get the following error:

Traceback (most recent call last):
File "/path/file.py", line 22, in <module>
symbolic_sum(k,k,0,10)
File "/other_path/calculus.py", line 620, in symbolic_sum
raise TypeError("need a summation variable")
TypeError: need a summation variable