Writing a list with nested tuples to a csv file

Question

I have a list with nested tuples, like the one below:

data = [('apple', 19.0, ['gala', '14', 'fuji', '5', 'dawn', '3', 'taylor', '3']),
 ('pear', 35.0, ['anjou', '29', 'william', '6', 'concorde', '4'])]

I want to flatten it out so that I can write a .csv file in which each item on every list corresponds to a column:

apple    19.0,   gala   14   fuji    5 dawn     3 taylor 3
pear     35.0    anjou  29   william 6 concorde 4

I tried using simple flattening:

flattened = [value for pair in data for value in pair]

But the outcome has not been the desired one. Any ideas on how to solve this?

Martijn Pieters · Accepted Answer · 2013-11-19 19:21:46Z

3

To write out the data to CSV, simply use the csv module and give it one row; constructing the row is not that hard:

import csv

with open(outputfile, 'w', newlines='') as ofh:
    writer = csv.writer(ofh)

    for row in data:
        row = list(row[:2]) + row[2]
        writer.writerow(row)

This produces:

apple,19.0,gala,14,fuji,5,dawn,3,taylor,3
pear,35.0,anjou,29,william,6,concorde,4

edited Nov 19, 2013 at 19:21

answered Nov 19, 2013 at 19:14

Martijn Pieters

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shad0w_wa1k3r · Accepted Answer · 2013-11-19 19:06:03Z

Disclaimer - Not very efficient Python code.

But, it does the job. (You can adjust the width (currently 10))

data = [('apple', 19.0, ['gala', '14', 'fuji', '5', 'dawn', '3', 'taylor', '3']),
        ('pear', 35.0, ['anjou', '29', 'william', '6', 'concorde', '4'])]

flattened = list()
for i, each in enumerate(data):
    flattened.append(list())
    for item in each:
        if isinstance(item, list):
            flattened[i].extend(item)
        else:
            flattened[i].append(item)
# Now print the flattened list in the required prettified manner.
for each in flattened:
    print ("".join(["{:<10}".format(item) for item in each]))
    # String is formatted such that all items are width 10 & left-aligned

Note - I tried to write the function for a more general case.
PS - Any code suggestions are welcome. I really want to improve this one.

PearsonArtPhoto · Accepted Answer · 2013-11-19 19:12:16Z

0

This seems like it calls for recursion

def flatten(inlist):
    outlist=[]
    if isinstance(inlist, (list, tuple)):
        for item in inlist:
            outlist+=flatten(item)
    else:
        outlist+=[inlist]
    return outlist

This should work no matter how nested your list becomes. Tested it with this:

>>> flatten([0,1,2,[3,4,[5,6],[7,8]]])
[0, 1, 2, 3, 4, 5, 6, 7, 8]

answered Nov 19, 2013 at 19:12

PearsonArtPhoto

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