Assertion none when checking column names of a dataframe

Question

I want to check that the columns of my data frame are in the right order. I used this code

def validation_columns(self)
header_input = list(self.data.columns)
assert header_input == ['column1','column2'], log.log_message("ERROR:...")

# log.log_message() is a function to print info in a log.txt file

Why do I get the error

AssertionError: None

Answer 1

The second argument to the assert keyword is not code to be run in the case of a False condition, it is a message to display in the case of a False condition. Because the function log.log_message(...) does not return anything, None is printed.

If you want to print text to a file if the condition is False, just use a normal if statement:

def validation_columns(self):
    header_input = list(self.data.columns)
    if header_input != ['column1','column2']:
        log.log_message("ERROR:...")