Read in a CSV file in lower case with Python

Question

I'm reading a CSV file into a namedtuple as so:

import csv
from collections import namedtuple

#So we can handle bad CSV files gracefully
def unfussy_reader(reader):
    while True:
        try:
            yield next(reader.lower())

        # This is a bad row that has an error in it (csv.Error)
        # Alternately it may be a line that doesn't map to the structure we've been given (TypeError)
        except (csv.Error, TypeError):
            pass

        continue

# Create the CSV reader object
csv_reader = csv.reader(file_stream, delimiter=' ', quotechar='"', escapechar='^')

# Set up the named tuple
csvline = namedtuple('csv_line', 'field1, field2, field3')

# Create the named tuple mapping object
map_to_tuple = map(csvline._make, csv_reader)

for line in unfussy_reader(map_to_tuple):
    # do stuff

This works well, but my problem is - I want all of the content of the CSV to be read in lower-case. As per this question, a simple lambda would do it: map(lambda x:x.lower(),["A","B","C"]) but I can't find anywhere to put it before the data ends up in the tuple (and thus unchaneable).

Is there a way to do this within this structure (Python 3.5)?

Answer 1

You can apply the lower transform to the stream before you create a CSV reader for it.

lower_stream = (line.lower() for line in file_stream)
csv_reader = csv.reader(lower_stream, delimiter=' ', quotechar='"', escapechar='^')

The parentheses around the lower_stream assignment target designate a generator expression. It will not use up file_stream and will not pull all of file_stream into memory.