[Python-ideas] CSV api with conversion

Denis Kolodin deniskolodin at gmail.com
Sun Apr 11 12:28:16 CEST 2010

My name is Denis Kolodin. I live in Russia, Tambov.
I was developing much time with C, Java, C#, R. But two month ago I'm using
It's really cool. Now, I move ALL my projects to it fully and have some
ideas which API's
extensions may will be useful.
The first thing I want to say about is an extension of CSV api. In R
language I could to set types for
the every column in a csv file. I propose to add a same function to the
Python's standard library.
Here it is (Python 3 version):

import csv
def reader2(csvfile, frame, *delimiter**=**';'*, **fmtparams):
    reader = csv.reader(csvfile, delimiter=delimiter, **fmtparams)
    for row in reader:
        l = min(len(row), len(frame))
        yield [frame[idx](row[idx]) for idx in range(l)]

This's generator function which converts an every column to the associated
In *frame *argument you must to set tuple/list of functions which will uses
convert values in same positions of row from csv file. Frame looks like list
of types )))
By default it uses ';' delimiter to make float values conversion are

As a sample you have the csv file like:
*Any spam...; 1; 2.0; 3*

I've saved it to "sample.csv" :)

If you are using function reader in the standard "csv" module you get rows
as a list of strings :(
*>>> reader = csv.reader(open("sample.csv"), delimiter=";")*
*>>> print(next(reader))*
*['Any spam...', ' 1', ' 2.0', ' 3']*
It's not bad in certan situatiuons. But with "reader2" function you can get
a list with necessary types:

>>> reader = reader2(open("foodstuffs.csv"), (str, int, float, int))
>>> print(next(reader))
['Any spam...', 1, 2.0, 3]

Now you can work with items without extra conversions. [?]
I think it's good to add this function to the standard library. I've already
used it many times.
This function can be useful for many people who works with csv files.
And I suppose it conforms to "batteries included" philosophy.

What do you think about this extension?
Is it possible to add this function to standard library or to add the same
behavior to
the standard "readed" function
in "csv" Python's module?

Best Regards,
Denis Kolodin
Russia, Tambov
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