CODEWITHSUNDEEP
pythoncsvdictionary
bojo
bojo

Reputation: 461

Python Dictionary to CSV

I have written code to read a CSV into a python dictionary, which works fine. I'm trying to get the dictionary back to a CSV. I have written the following:

import csv

itemDict={}

listReader = csv.reader(open('/Users/broberts/Desktop/Sum_CSP1.csv','rU'), delimiter = ',', quotechar='|')

for row in listReader:
    fID = row[0]
    fClassRange = row[1]
    fArea = row[2]

    if itemDict.has_key(fID):
        itemDict[fID][fClassRange]=fArea
    else:
        itemDict[fID] = {'5.0 to 5.25':'','5.25 to 5.5':'','5.5 to 5.75':'','5.75 to 6.0':'','6.0 to 6.25':'','6.25 to 6.5':'','6.5 to 6.75':'','6.75 to 7.0':'','7.0 to 7.25':'','7.25 to 7.5':'','7.5 to 7.75':'','7.75 to 8.0':'','8.0 to 8.25':'',}
        itemDict[fID][fClassRange]=fArea

listWriter = csv.writer(open('/Users/broberts/Desktop/Sum_CSP1_output.csv', 'wb'), delimiter=',', quotechar='|', quoting=csv.QUOTE_MINIMAL)

for a in itemDict:
    print a
    listWriter.writerow(a)

In the last block, listWriter will not write anything to the CSV though it will print a. I believe this has something to do with a dictionary being unordered. I really need to write out the fID and each of the keys associated with each fID (fClassRange ex. "5.0 to 5.25") and then the value fArea associated with each fClassRange to the CSV, but I haven't even gotten that far in my code since I can't figure out how to write out even the fID.

I looked into using DictWriter, but I can't figure out how to tell it what the required fieldnames are.

Upvotes: 46

Views: 60456

Answers (8)

Duck Ling
Duck Ling

Reputation: 2170

What helped me was adding newline="" argument when opening file.

ex:

with open("sample.csv", "w", newline="") as outfile:
    writer = csv.writer(outfile)
    for num in range(0, 10):
        writer.writerow([num])

src

Upvotes: 1

Marcin
Marcin

Reputation: 239005

An example with writerows:

import csv

def main():

    results = [
            {'File': 'test.txt', 'Temperature': 32.33, 'Day': 'Monday'},
            {'File': 'test2.txt', 'Temperature': 44.33, 'Day': 'Tuesday'},
            {'File': 'test3.txt', 'Temperature': 44.23, 'Day': 'Sunday'}
        ]

    with open('results.csv', 'w') as f:  
        w = csv.DictWriter(f, results[0].keys())
        w.writeheader()        
        w.writerows(results)                    
        
if __name__ == "__main__":
    main()

which will result in results.csv of:

File,Temperature,Day
test.txt,32.33,Monday
test2.txt,44.33,Tuesday
test3.txt,44.23,Sunday

Upvotes: 6

Voilin
Voilin

Reputation: 401

d = [{'a': 1, 'b': 2},{'a': 3, 'b': 4}]

with open('csv_file.csv', 'w', newline='\n') as f:
    w = csv.DictWriter(f, d[0].keys())
    w.writeheader()
    for i in d:
        w.writerow(i)

gets you

a,b
1,2
3,4

Upvotes: 0

Spencer Rathbun
Spencer Rathbun

Reputation: 14910

The default writer expects a list, which is why it won't work for you. To use the dictwriter, just change your listwriter = line to this:

with open('/Users/broberts/Desktop/Sum_CSP1_output.csv', 'wb') as outfile:
    listWriter = csv.DictWriter(
       outfile,
       fieldnames=itemDict[itemDict.keys()[0]].keys(),
       delimiter=',',
       quotechar='|',
       quoting=csv.QUOTE_MINIMAL
    )

Or, you can just set fieldnames to be fieldnames=['arbitrary','list','of','keys'] if you know what the fields are supposed to be.

Upvotes: 28

Lucifer
Lucifer

Reputation: 305

Easiest Way

You can convert the dictionary into Dataframe and write it to csv Eg

import pandas as pd
my_dict = {"tester": 1, "testers": 2}
df=pd.DataFrame(my_dict,index=[0])
df.to_csv("path and name of your csv.csv")

output

   tester  testers
0       1        2

Upvotes: -1

Jeff
Jeff

Reputation: 495

Sample data:

mydict = [{"col1": 1000, "col2": 2000}, {"col1": 3000, "col2": 4000}]

One-liner for converting a list of dicts to CSV, using pandas: 

import pandas as pd

pd.DataFrame(mydict).to_csv('out.csv', index=False)

Results:

col1,col2
1000,2000
3000,4000

Upvotes: 36

Francis Kessie
Francis Kessie

Reputation: 51

This is what i use, its simple and works fine for me. when you have only one dictionary, use this

my_dict = {"tester": 1, "testers": 2}
with open('mycsvfile.csv', 'wb') as f:  
    w = csv.DictWriter(f, my_dict.keys())
    w.writerow(dict((fn,fn) for fn in my_dict.keys()))
    w.writerow(my_dict)

$ cat mycsvfile.csv
testers,tester
2,1

When you have a list of dictionaries, like what you get from SQL queries, you do like this.

my_dict = ({"tester": 1, "testers": 2},{"tester": 14, "testers": 28})
with open('mycsvfile.csv', 'wb') as f:  
    w = csv.DictWriter(f, my_dict[0].keys())
    w.writerow(dict((fn,fn) for fn in my_dict[0].keys()))
    w.writerows(my_dict)

cat mycsvfile.csv
testers,tester
2,1
28,14

Upvotes: 3

Arjen
Arjen

Reputation: 11

For posterity:

You should use iteritems() to iterate over a dictionary, so the last part becomes

for name, values in itemDict.iteritems():
    print values
    listWriter.writerow(values)

Upvotes: 1

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