How to create a dictionary from a line of text?

by

In Python 2 you could use izip in the itertools module and the magic of generator objects to write your own function to simplify the creation of pairs of values for the dict records. I got the idea for pairwise() from a similarly named (although functionally different) recipe in the Python 2 itertools docs.

To use the approach in Python 3, you can just use plain zip() since it does what izip() did in Python 2 resulting in the latter’s removal from itertools — the example below addresses this and should work in both versions.

try:
    from itertools import izip
except ImportError:  # Python 3
    izip = zip

def pairwise(iterable):
    "s -> (s0,s1), (s2,s3), (s4, s5), ..."
    a = iter(iterable)
    return izip(a, a)

Which can be used like this in your file reading for loop:

from sys import argv

records = {}
for line in open(argv[1]):
    fields = (field.strip() for field in line.split(','))  # generator expr
    record = dict(pairwise(fields))
    records[record['TSN']] = record

print('Found %d records in the file.' % len(records))

But wait, there’s more!

It’s possible to create a generalized version I’ll call grouper(), which again corresponds to a similarly named itertools recipe (which is listed right below pairwise()):

def grouper(n, iterable):
    "s -> (s0,s1,...sn-1), (sn,sn+1,...s2n-1), (s2n,s2n+1,...s3n-1), ..."
    return izip(*[iter(iterable)]*n)

Which could be used like this in your for loop:

    record = dict(grouper(2, fields))

Of course, for specific cases like this, it’s easy to use functools.partial() and create a similar pairwise() function with it (which will work in both Python 2 & 3):

import functools
pairwise = functools.partial(grouper, 2)

Postscript

Unless there’s a really huge number of fields, you could instead create a actual sequence out of the pairs of line items (rather than using a generator expression which has no len()):

fields = tuple(field.strip() for field in line.split(','))

The advantage being that it would allow the grouping to be done using simple slicing:

try:
    xrange
except NameError:  # Python 3
    xrange = range

def grouper(n, sequence):
    for i in xrange(0, len(sequence), n):
        yield sequence[i:i+n]

pairwise = functools.partial(grouper, 2)

More Related Contents:

  1. Creating a tree/deeply nested dict from an indented text file in python
  2. how to parse the response in python?
  3. Creating multiple python dictionaries from a file
  4. How to parse data in JSON format?
  5. Why can’t I use a list as a dict key in python?
  6. How can I get list of values from dict?
  7. heapq with custom compare predicate
  8. What is the fastest way to parse large XML docs in Python?
  9. how to iterate through dictionary in a dictionary in django template?
  10. How to check if one dictionary is a subset of another larger dictionary?
  11. Subclassing Python dictionary to override __setitem__
  12. switching keys and values in a dictionary in python [duplicate]
  13. OrderedDict vs defaultdict vs dict [closed]
  14. Is there a built in package to parse html into dom?
  15. Python – sum values in dictionary
  16. Parsing SQL with Python
  17. How to json_normalize a column with NaNs
  18. JSON dumps custom formatting
  19. Nested dictionary value from key path
  20. parsing nested parentheses in python, grab content by level
  21. How to make a dictionary that returns key for keys missing from the dictionary instead of raising KeyError?
  22. parsing a fasta file using a generator ( python )
  23. Iterating through a JSON object
  24. Appending to list in Python dictionary [duplicate]
  25. Converting xml to dictionary using ElementTree
  26. Mapping dictionary value to list
  27. How to change all the dictionary keys in a for loop with d.items()?
  28. Python string operation, extract text between html tags
  29. Slicing a dictionary
  30. Random Python dictionary key, weighted by values

Leave a Comment