Writing a dictionary to a csv file with one line for every 'key: value'

Easiest way is to ignore the csv module and format it yourself.

with open('my_file.csv', 'w') as f:
    [f.write('{0},{1}\n'.format(key, value)) for key, value in my_dict.items()]

Just to give an option, writing a dictionary to csv file could also be done with the pandas package. With the given example it could be something like this:

mydict = {'key1': 'a', 'key2': 'b', 'key3': 'c'}

import pandas as pd

(pd.DataFrame.from_dict(data=mydict, orient='index')
   .to_csv('dict_file.csv', header=False))

The main thing to take into account is to set the 'orient' parameter to 'index' inside the from_dict method. This lets you choose if you want to write each dictionary key in a new row.

Additionaly, inside the to_csv method the header parameter is set to False just to have only the dictionary elements without annoying rows. You can always set column and index names inside the to_csv method.

Your output would look like this:

key1,a
key2,b
key3,c

If instead you want the keys to be the column's names, just use the default 'orient' parameter that is 'columns', as you could check in the documentation links.

The DictWriter doesn't work the way you expect.

with open('dict.csv', 'w') as csv_file:  
    writer = csv.writer(csv_file)
    for key, value in mydict.items():
       writer.writerow([key, value])

To read it back:

with open('dict.csv') as csv_file:
    reader = csv.reader(csv_file)
    mydict = dict(reader)

which is quite compact, but it assumes you don't need to do any type conversion when reading

outfile = open( 'dict.txt', 'w' )
for key, value in sorted( mydict.items() ):
    outfile.write( str(key) + '\t' + str(value) + '\n' )