No removal of null values (Python)

Question

For processing the content of multiple CSV files, I have to filter several characters, most notably NULL values, from string-list-elements. For this I've tried several solutions from the web. One of them is the following function:

def removeNull(rawString):
    l = filter("\u0000", list(rawString))
    newString = ''.join(l)
    printUtil.printAll(newString, "\n")
    return newString

However, it always gives me TypeError: 'str' object is not callable, terminating the program. The more sophisticated solutions didn't gave me an error but they changed absolutely nothing and the NULL values where still in place.

Furthermore, if I exchange \u0000 by any other value but None (which results in no changes), I am getting the same error message.

Hopefully, someone can solve this for me for I am out of ideas after 4 or 5 hours of trial and error.

Thank you for your answers and suggestions!

Solving the problem:

The error message originated from the fact, that I used "\u0000" as argument for the build in filter-function. Two valid solutions to that particular problem focus on passing the necessary function:

l = filter(lambda x: x != '\u0000',rawString)

or

l = filter(lambda x:ord(x) != 0, list(rawString))

mgilson · Accepted Answer · 2013-04-17 16:31:20Z

1

filter expects the first argument to be a function (or, more precisely a callable). It then iterates over the second argument, passing each to the function. Where the function returns a False-like value, it is skipped in the output.

You could try:

l = filter(lambda x: x != '\u0000',rawString)

answered Apr 17, 2013 at 16:31

mgilson

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2 Comments

Florian R. Klein Over a year ago

This removes the null-values. However, for the given input it returns gibberish afterwards. I have no idea why writing the filtered content of the file is totally different from the original and from the console ouput when only null-values should be deleted. I can upload my in- and output files if needed to make it more clear what happened. Edit: The same goes for Joran Beasleys solution.

Florian R. Klein Over a year ago

For some clarification: The string which goes into the removal function behaves like a byte-array when saving it to a file, at least i have to go into binary writing mode. Unfortunately I do not understand this outcome too well but at least it works now.

Joran Beasley · Accepted Answer · 2013-04-17 16:31:07Z

0

l = filter(lambda x:ord(x) != 0, list(rawString))

should work better

to make it more transparent

def is_not_null(ch):
    return ch != u'\u0000'

print filter(is_not_null,list(rawString))

answered Apr 17, 2013 at 16:31

Joran Beasley

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2 Comments

Florian R. Klein Over a year ago

The result appears to be correct in the console window, however there are unexpected problems when saving this to a file (see my respont to the solution of mgilson).

Florian R. Klein Over a year ago

I will have to look into that later. Thanks to both of you the final solution might be near.

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