Suddenly receiving TypeError ( 'str' object is not callable ) in all of my scripts

Yesterday my scripts were working fine. Today I am getting TypeError ( 'str' object is not callable ) in every script that uses str().
Simple example:

for i in range(0,5):
    print('i is ' + str(i))

[error] script [ sikulitemp-5042484742757321256 ] stopped with error in line 2
[error] TypeError ( 'str' object is not callable )
[error] --- Traceback --- error source first
line: module ( function ) statement
2: main ( <module> ) print('i is ' + str(i))
[error] --- Traceback --- end --------------

I've tried rebooting, but no help.
Nothing was updated overnight as far as I know.