CODEWITHSUNDEEP
pythondictionary
Vlad
Vlad

Reputation: 19

Adding dictionary keys and values after line split?

If I have for instance the file:

;;;
;;;
;;;
A  1 2 3
B  2 3 4
C  3 4 5

And I want to read it into a dictionary of {str: list of str} :

{'A': ['1', '2', '3'], 'B': ['2', '3', '4'], 'C': ['3', '4', '5']

I have the following code:

d = {}
with open('file_name') as f:
    for line in f:
        while ';;;' not in line:
            (key, val) = line.split('  ')
        #missingcodehere    
return d

What should I put in after the line.split to assign the keys and values as a str and list of str?

Upvotes: 1

Views: 2253

Answers (2)

idjaw
idjaw

Reputation: 26600

To focus on your code and what you are doing wrong.

You are pretty much in an infinite loop with your while ';;;' not in line. So, you want to change your logic with how you are trying to insert data in to your dictionary. Simply use a conditional statement to check if ';;;' is in your line.

Then, when you get your key and value from your line.strip().split(' ') you simply just assign it to your dictionary as d[key] = val. However, you want a list, and val is currently a string at this point, so call split on val as well.

Furthermore, you do not need to have parentheses around key and val. It provides unneeded noise to your code.

The end result will give you:

d = {}
with open('new_file.txt') as f:
    for line in f:
        if ';;;' not in line:
            key, val = line.strip().split('  ')
            d[key] = val.split()

print(d)

Using your sample input, output is:

{'C': ['3', '4', '5'], 'A': ['1', '2', '3'], 'B': ['2', '3', '4']}

Finally, to provide an improvement to the implementation as it can be made more Pythonic. We can simplify this code and provide a small improvement to split more generically, rather than counting explicit spaces: 

with open('new_file.txt') as fin:
    valid = (line.split(None, 1) for line in fin if ';;;' not in line)
    d = {k:v.split() for k, v in valid}

So, above, you will notice our split looks like this: split(None, 1). Where we are providing a maxsplit=1.

Per the docstring of split, it explains it pretty well:

Return a list of the words in S, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done. If sep is not specified or is None, any whitespace string is a separator and empty strings are removed from the result.

Finally, we simply use a dictionary comprehension to obtain our final result.

Upvotes: 4

donkopotamus
donkopotamus

Reputation: 23206

Why not simply:

def make_dict(f_name):
    with open(f_name) as f:
        d = {k: v.split() 
             for k, v in [line.strip().split('  ') 
                          for line in f 
                          if ';;;' not in line]}

    return d

Then 

>>> print(make_dict('file_name'))
{'A': ['1', '2', '3'], 'B': ['2', '3', '4'], 'C': ['3', '4', '5']}

Upvotes: 0

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