python: modifying dictionary to string

Question

Below is the code I got. However, I don't know how to get rid of the last comma. I just want the key separated from the value with a space, and then a comma after it to separate it from the next key.

Also, a question on files. If I open a file and read it, and want to read the file again, is there no way to get the cursor to the beginning of the file without closing and opening the file again?

def dict_to_str(d):
    """ (dict) -> str

    Return a string containing each key and value in d. Keys and
    values are separated by a blank space. Each key-value pair is
    separated by a comma. 

    >>> dict_to_str({3: 4, 5: 6})
    '3 4,5 6'
    """ 
    s = ''
    for (k, v) in d.items:
        s = s + str(k) + " " + str(v) + ','
    return s

Please separate your questions into separate entries. It would be hard to find proper answer, if you have two completely different questions. Also it won't be very useful for others. What is the connection between converting dict to string and changing position in file without reopening? — Tadeck
– Tadeck, Commented Jul 17, 2013 at 4:48
Just thought I'd squeeze another question in there while I'm at it. Sorry, will keep in mind for next time! — user2489861
– user2489861, Commented Jul 17, 2013 at 4:59
Well, it is okay if the question is related to the main one (even loosely). But in your case it looks like it was not. Please read faq - it has some nice explanation on what format of questions is best fit for SO. — Tadeck
– Tadeck, Commented Jul 17, 2013 at 5:04

Blender · Accepted Answer · 2013-07-17 04:44:51Z

4

Use join instead:

return ', '.join([str(key) + ' ' + str(value) for key, value in d.items()])

Or more verbosely:

items = []

for key, value in d.items():
    items.append('{0} {1}'.format(key, value))

return ', '.join(items)

As for the file, you can seek back to the beginning:

handle.seek(0)

answered Jul 17, 2013 at 4:44

Blender

300k55 gold badges462 silver badges512 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

kevinsa5 Over a year ago

Lovely line. It's things like your first example that make me love python.

Tadeck Over a year ago

@Blender: Any reason it is return ', '.join([str(key) + ' ' + str(value) for key, value in d.items()]) instead of return ', '.join(str(key) + ' ' + str(value) for key, value in d.items()) (second example does not create list in between)?

Blender Over a year ago

@Tadeck: ' '.join() is faster with a list comprehension, as it has a definite size. I don't remember the actual reason, but something about join having to allocate memory for the string.

Tadeck Over a year ago

@Blender: You seem to be right (proof: ideone.com/GsUTrk). Thanks for clarification.

Sukrit Kalra · Accepted Answer · 2013-07-17 04:50:14Z

2

Just return all of the string except the last character, like so -

def dict_to_str(d):
    """ (dict) -> str

    Return a string containing each key and value in d. Keys and
    values are separated by a blank space. Each key-value pair is
    separated by a comma. 

    >>> dict_to_str({3: 4, 5: 6})
    '3 4,5 6'
    """ 
    s = ''
    for (k, v) in d.items():
        s += str(k) + " " + str(v) + ','
    return s[:-1]

Output Test -

>>> dict_to_str({1:2, 3:4})
'1 2,3 4'

P.S - d.items is a function and you cannot iterate over it, you need to call the function and iterate over the returned list.

For your other question, you can just do fileVar.seek(0)

edited Jul 17, 2013 at 4:50

answered Jul 17, 2013 at 4:44

Sukrit Kalra

34.7k7 gold badges73 silver badges71 bronze badges

2 Comments

user2489861 Over a year ago

Ah! Forgot I could use slicing. Your solution is great, much appreciated! :)

Sukrit Kalra Over a year ago

Glad to be of help. :)

Collectives™ on Stack Overflow

python: modifying dictionary to string

2 Answers 2

4 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related