Text to dictionary doesn't work

Question

I have the following text file in the same folder as my Python Code.

78459581
Black Ballpoint Pen
12345670
Football
49585922
Perfume
83799715
Shampoo

I have written this Python code.

file = open("ProductDatabaseEdit.txt", "r")
d = {}
for line in file:
    x = line.split("\n")
    a=x[0]
    b=x[1]
    d[a]=b

print(d)

This is the result I receive.

b=x[1]  # IndexError: list index out of range

My dictionary should appear as follows:

{"78459581" : "Black Ballpoint Pen"
 "12345670" : "Football"
 "49585922" : "Perfume"
 "83799715" : "Shampoo"}

What am I doing wrong?

Bob, for those of us who are not clairvoyant, it may be clearer if you describe what you wish to accomplish in the first paragraph{.} — boardrider, Jul 11 '16 at 11:01

L3viathan · Answer 1 · 2016-07-10T12:51:26.143

5

A line is terminated by a linebreak, thus line.split("\n") will never give you more than one line.

You could cheat and do:

for first_line in file:
    second_line = next(file)

edited Jul 10 '16 at 12:51

answered Jul 10 '16 at 12:46

L3viathan

26,748
2
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2

I'd not call it cheating, by the way ;-) Using `next()` is an excellent solution. – Martijn Pieters Jul 10 '16 at 13:00
I called it cheating, because it breaks if the assumption (even number of lines) is violated. But I guess in that case, unless something is planned specifically, it *should* break. – L3viathan Jul 10 '16 at 13:19
1

Exactly; and you can always use `next(file, )` if a missing last line is not an error. – Martijn Pieters Jul 10 '16 at 13:21
Actually, it probably (haven't tested it) won't break, since `next(file)` will raise `StopIteration` and just break out of the loop. – L3viathan Jul 10 '16 at 13:21
@L3viathan this is what I have done. `for first_line in file: [NEW LINE] second_line = next(file) [NEW LINE] d[first_line] = second_line` but this gives me this dictionary: `'78459581\n': 'Black Ballpoint Pen \n'` - how do I remove the `\n`? – vik1245 Jul 10 '16 at 13:36
@BobSmith: use `str.rstrip()`. – Martijn Pieters Jul 10 '16 at 13:46
Fantastic! Thanks very much @MartijnPieters – vik1245 Jul 10 '16 at 13:48

ifma · Answer 2 · 2016-07-10T13:13:04.730

You can simplify your solution by using a dictionary generator, this is probably the most pythonic solution I can think of:

>>> with open("in.txt") as f:
...   my_dict = dict((line.strip(), next(f).strip()) for line in f)
... 
>>> my_dict
{'12345670': 'Football', '49585922': 'Perfume', '78459581': 'Black Ballpoint Pen', '83799715': 'Shampoo'}

Where in.txt contains the data as described in the problem. It is necessary to strip() each line otherwise you would be left with a trailing \n character for your keys and values.

joel goldstick · Accepted Answer · 2016-07-10T13:39:50.990

2

You need to strip the \n, not split

file = open("products.txt", "r")
d = {}
for line in file:
    a = line.strip()
    b = file.next().strip()
    # next(file).strip() # if using python 3.x
    d[a]=b

print(d)

{'12345670': 'Football', '49585922': 'Perfume', '78459581': 'Black Ballpoint Pen', '83799715': 'Shampoo'}

edited Jul 10 '16 at 13:39

answered Jul 10 '16 at 13:04

joel goldstick

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6
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Your solution provides this error... `AttributeError: '_io.TextIOWrapper' object has no attribute 'next'` – vik1245 Jul 10 '16 at 13:34
It produced the results shown. hmm. I used python 2.7 – joel goldstick Jul 10 '16 at 13:35
I am using Python 3.4 (or something close to it) – vik1245 Jul 10 '16 at 13:38
I found this: In Python 3, use `next(file)` instead of `file.next()`. – joel goldstick Jul 10 '16 at 13:39
It works, but this gives me the next error. `StopIteration` for the line `b = next(file).strip()` – vik1245 Jul 10 '16 at 13:41
I just changed my code and ran with python 3.4. I didn't get that error – joel goldstick Jul 10 '16 at 13:43
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/116926/discussion-between-joel-goldstick-and-bob-smith). – joel goldstick Jul 10 '16 at 13:44

score 1 · Answer 4 · answered Jul 10 '16 at 13:57

What's going on

When you open a file you get an iterator, which will give you one line at a time when you use it in a for loop.

Your code is iterating over the file, splitting every line in a list with \n as the delimiter, but that gives you a list with only one item: the same line you already had. Then you try to access the second item in the list, which doesn't exist. That's why you get the IndexError: list index out of range.

How to fix it

What you need is this:

file = open('products.txt','r')
d = {}
for line in file:
    d[line.strip()] = next(file).strip()

In every loop you add a new key to the dictionary (by assigning a value to a key that didn't exist yet) and assign the next line as the value. The next() function is just telling to the file iterator "please move on to the next line". So, to drive the point home: in the first loop you set first line as a key and assign the second line as the value; in the second loop iteration, you set the third line as a key and assign the fourth line as the value; and so on.

The reason you need to use the .strip() method every time, is because your example file had a space at the end of every line, so that method will remove it.

Or...

You can also get the same result using a dictionary comprehension:

file = open('products.txt','r')
d = {line.strip():next(file).strip() for line in file}

Basically, is a shorter version of the same code above. It's shorter, but less readable: not necessarily something you want (a matter of taste).

score 0 · Answer 5 · edited May 23 '17 at 12:17

In my solution i tried to not use any loops. Therefore, I first load the txt data with pandas:

import pandas as pd
file = pd.read_csv("test.txt", header = None)

Then I seperate keys and values for the dict such as:

keys, values = file[0::2].values, file[1::2].values

Then, we can directly zip these two as lists and create a dict:

result = dict(zip(list(keys.flatten()), list(values.flatten())))

To create this solution I used the information as provided in [question]: How to remove every other element of an array in python? (The inverse of np.repeat()?) and in [question]: Map two lists into a dictionary in Python

score 0 · Answer 6 · answered Jul 10 '16 at 13:14

0

You can loop over a list two items at a time:

file = open("ProductDatabaseEdit.txt", "r")
data = file.readlines()
d = {}

for line in range(0,len(data),2):
    d[data[i]] = data[i+1]

answered Jul 10 '16 at 13:14

Tim

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score 0 · Answer 7 · answered Jul 11 '16 at 11:19

Try this code (where the data is in /tmp/tmp5.txt):

#!/usr/bin/env python3

d = dict()
iskey = True
with open("/tmp/tmp5.txt") as infile:
    for line in infile:
        if iskey:
            _key = line.strip()
        else:
            _value = line.strip()
            d[_key] = _value
        iskey = not iskey

print(d)

Which gives you:

{'12345670': 'Football', '49585922': 'Perfume', '78459581': 'Black Ballpoint Pen', '83799715': 'Shampoo'}

Text to dictionary doesn't work

7 Answers7

What's going on

How to fix it

Or...