output and input dictionary

Question

Hi I want to save a dictionary to csv, then input it. However on both output and input, I met some issues.

For output I tried: (D_FINAL is the dictionary)

f = open("D_FINAL.csv", "w")
writer = csv.writer(f)
for k, v in D_FINAL.items():
    writer.writerow([k, v])
f.close

It works fine but when I want to open the csv, it says the file is locked from editting

For input I tried

import csv
dict = {}
r = open('D_FINAL3.csv', 'r')
for k, v in csv.reader(r):
    dict[k] = v

r.close()

but I got error

ValueError                                Traceback (most recent call last)
<ipython-input-92-d3e2b3081317> in <module>()
      3 dict = {}
      4 r = open('D_FINAL2.csv', 'r')
----> 5 for k, v in csv.reader(r):
      6     dict[k] = v
      7     
ValueError: not enough values to unpack 
(expected 2, got 0)

What's the correct way to do these ?

You are not calling `f.close()`, without the parentheses `f.close` is a no-op. — cdarke, Aug 28 '18 at 07:33
Even better than calling `close()` by hand, use a [with block](https://stackoverflow.com/a/3012565/962190) to open/close your file. — Arne, Aug 28 '18 at 07:34
Did you try same operation on output and input...? Maybe the code is not relevant on "For input I tried". — greentec, Aug 28 '18 at 07:34

Jean-François Fabre · Accepted Answer · 2018-08-28T08:06:16.370

on windows (python 3), if you don't use open("D_FINAL.csv", "w",newline=""), the resulting csv file has extra blank lines (because of the extra carriage return char inserted making end of lines like \r\r\n).

Unfortunately, those double carriage return chars are read back not the same way: it generates a blank row after each valid data row. So unpacking fails because there aren't any elements in the row.

More on this nasty side-effect: CSV file written with Python has blank lines between each row

So when reading, you get a blank line.

Just do (and upgrade your python skills a notch):

with open("D_FINAL.csv", "w", newline="")  as f:  # python 2: use: "wb"
    writer = csv.writer(f)
    writer.writerows(D_FINAL.items())

(write in one go with writerows, use a with block so you don't miss the call to close and the file isn't locked anymore)

Note that json module is best suited to read & write dictionaries (if your need is serialization)

Aside: it's better to read back using a better technique too (it seems that the newline thingy isn't really necessary when reading):

with open("D_FINAL.csv", "r", newline="")  as f:  # python 2: use: "rb"
    writer = csv.reader(f)
    output = {k:v for k,v in writer}  # unpack+dictionary comprehension

Radan · Answer 2 · 2018-08-28T07:42:05.440

1

Looking at the code you have given, it seems like you are not actually closing the file by calling f.close(). Changing f.close to f.close() should help you get over this issue. But remember you can improve your code by implementing a with block. for example,

with open("D_FINAL.csv", "w",newline="") as f:
    writer = csv.writer(f)
    for k, v in D_FINAL.items():
        writer.writerow([k, v])

edited Aug 28 '18 at 07:42

answered Aug 28 '18 at 07:39

Radan

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`open("D_FINAL.csv", "w")` isn't the proper way of writing a csv file. – Jean-François Fabre Aug 28 '18 at 07:41
@Jean-FrançoisFabre i just modified the code from question, so its easy for them to understand. i took your advice and changed it now. :) cheers! – Radan Aug 28 '18 at 07:42

score 0 · Answer 3 · answered Aug 28 '18 at 07:41

0

May be you can use pandas for this purpose

import pandas as pd
pd.DataFrame.from_dict(data=D_FINAL, orient='index').to_csv('D_FINAL.csv')

Hope this helps.

answered Aug 28 '18 at 07:41

Shrey

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output and input dictionary

3 Answers3