Python 3.6+，更改文件中无的表示

Question

I have to extract from several sources and save the result to csv files. When the data received for a field is None , I want it represented as empty string. (I realize I'll lose the distinction between empty string and NULL-type values in the source.)

My underlying requirement is to preserve the distinction between the string "None" and nothingness in a plain delimited file, without using quotes.

I hope to avoid calling a function that checks if a value is null for every nullable field I write, or at least have that call not explicit in the code... eg, I want to just code f.write(row['LastName'] , and if the LastName is "None" get "None", but if it is of NoneType get an empty string.

I haven't yet investigated if the comes-with csv library can do what I need, I will do that, it seems likely that's the easiest approach.

But: is there anything I can override, so that if I write None to a file, I get empty string (or something besides the string "None" in the output file?

It seems to me I'd have to change either 1) the built-in write method of _io.TextIOWrapper or 2) the __str__ method of the NoneType .

Answer 1

if row['LastName'] is None will check if your value is a NoneType

Something like:

if row['LastName'] is None:
    f.write("")
else:
    f.write(row['LastName'])

Would get the job done.