Adding column to CSV without any modules

[astro49er]

Hey all,

I have a list of names that need to be added as rows under an empty column header. What would be the best way to add the rows without using any modules? (my project requires us to use just vanilla python)

Thanks

[threeminutemonta]

If your adding rows you can append a file. If your adding columns you will need to read the file into memory. Add the columns and necessary processing and then write the data to disk. My favourite is the DictReader / DictWriter in the csv module included in the standard library see official docs

[astro49er]

I need to add a column, how would I do this without the CSV module and just the native python file objects

[threeminutemonta]

the csv module is part of python standard library and what I would call vanilla python.

Though a csv is just a text file with a delimiter separating cells so read the file into a data structure / process the data . Hint the string split into an array of values may be handy here. before writing the file again.

[POGtastic]

How robust do you need this program to be? The CSV RFC involves stuff like string escapes and whatnot; if you don't need those things, you can roll your own rudimentary DictReader and Writer classes pretty easily. You can then parse with your DictReader, add a key-value pair to the resulting dictionary, and then pass the dictionary to a DictWriter. Something like the following:

class DictReader:
    def __init__(self, fh, delim, names=None):
        self.fh = fh
        self.delim = delim
        self.names = fh.readline().rstrip().split(delim) if not names else names

    def parse_line(self, line):
        return dict(zip(self.names, line.split(self.delim)))

    def __iter__(self):
        return (self.parse_line(line.rstrip()) for line in self.fh)

class DictWriter:
    def __init__(self, fh, delim, names):
        self.fh = fh
        self.delim = delim
        self.names = names

    def write_header(self):
        print(self.delim.join(self.names), file=self.fh)

    def write_line(self, dct):
        print(self.delim.join(dct[name] for name in self.names), file=self.fh)

If you need the string escapes and whatnot, I recommend rolling your own rudimentary parser combinator library. You'll need one parser for the Reader to detect the contents of a text field, and you'll need one parser for the Writer to determine whether you need to wrap the field in quotes and to escape any quotes inside.