Python

File to dictionary

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Join Date: Oct 2009

Posts: 18

Reputation: pyprog is an unknown quantity at this point

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pyprog

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Newbie Poster

File to dictionary

Nov 3rd, 2009

If I have a file that has a content of this kind:
a,b
c,d
e,f
g,h

I need to make a list of the letters in the first column, i.e., [a, c, e, g]. I wrote some code which prints these letters but I don't know how to put them into a list. Here is the code:

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def file_to_dict(f):
    for line in f:
        columns = line.split(",")
        print columns[0]
def file_to_dict(f):
    for line in f:
        columns = line.split(",")
        print columns[0]

Your help is appreciated.

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Join Date: Jul 2009

Posts: 243

Reputation: masterofpuppets is an unknown quantity at this point

Solved Threads: 60

masterofpuppets masterofpuppets is offline

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Posting Whiz in Training

Nov 3rd, 2009

Hint:

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
>>> l = []
>>> l += [ "a" ]
>>> l
['a']
>>>
>>> l = []
>>> l += [ "a" ]
>>> l
['a']
>>>

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"My belief is stronger than your doubt."

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Join Date: Oct 2009

Posts: 18

Reputation: pyprog is an unknown quantity at this point

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pyprog

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Newbie Poster

Nov 3rd, 2009

•

Originally Posted by masterofpuppets

Hint:
Help with Code Tags

Python Syntax (Toggle Plain Text)
>>> l = []
>>> l += [ "a" ]
>>> l
['a']
>>>
>>> l = [] >>> l += [ "a" ] >>> l ['a'] >>>

I did the following

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def file_to_dict(f):
    list1 = []
    for line in f:
        columns = line.split(",")
        letters = columns[1]
    list1 += [letters]
    print list1
def file_to_dict(f):
    list1 = []
    for line in f:
        columns = line.split(",")
        letters = columns[1]
    list1 += [letters]
    print list1

but the output is just ['g']. It always prints only the last letter. How to print them all in a list?

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Join Date: Jul 2009

Posts: 243

Reputation: masterofpuppets is an unknown quantity at this point

Solved Threads: 60

masterofpuppets masterofpuppets is offline

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Posting Whiz in Training

Nov 3rd, 2009

hi again,
the problem is that you have to add the letter in the list while you are in the for loop

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
for line in f:
    columns = line.split(",")
    letters = columns[ 0 ]
    list1 += [ letters ]
for line in f:
    columns = line.split(",")
    letters = columns[ 0 ]
    list1 += [ letters ]

also I am not sure why you put columns[ 1 ], I thought you wanted the first element, which is columns[ 0 ]

My site ->> http://8masterofpuppets8.webs.com/
"My belief is stronger than your doubt."

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Join Date: Oct 2009

Posts: 18

Reputation: pyprog is an unknown quantity at this point

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pyprog

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Newbie Poster

Nov 3rd, 2009

•

Originally Posted by masterofpuppets

hi again,
the problem is that you have to add the letter in the list while you are in the for loop
Help with Code Tags

Python Syntax (Toggle Plain Text)
for line in f:
    columns = line.split(",")
    letters = columns[ 0 ]
    list1 += [ letters ]
for line in f: columns = line.split(",") letters = columns[ 0 ] list1 += [ letters ]
also I am not sure why you put columns[ 1 ], I thought you wanted the first element, which is columns[ 0 ]

yeah sorry...never mind the [1]...my mistake...thank you for your help...much appreciated...

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Join Date: Oct 2004

Posts: 4,151

Reputation: vegaseat is just really nice

Solved Threads: 952

vegaseat

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DaniWeb's Hypocrite

Nov 3rd, 2009

The more common approach would be to use append() ...

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
for line in f:
    columns = line.split(",")
    letters = columns[ 0 ]
    list1.append(letters)
for line in f:
    columns = line.split(",")
    letters = columns[ 0 ]
    list1.append(letters)

I think it is less mistake prone. I also want to point out, that should you want to read the second column (the end of each line), you will find a newline character attached.

Since you title is File to dictionary this may become important.

Last edited by vegaseat; Nov 3rd, 2009 at 5:00 pm. Reason: newline

May 'the Google' be with you!

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Join Date: Aug 2008

Posts: 184

Reputation: snippsat is an unknown quantity at this point

Solved Threads: 53

snippsat

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Junior Poster

Nov 3rd, 2009

To make it short with python list comprehensions.
Not that this make code better or more readable in many cases.
But think this line is not so bad to understand.

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
>>> f = [line[0] for line in open('ab.txt')]
>>> f
['a', 'c', 'e', 'g']
>>>
>>> f = [line[0] for line in open('ab.txt')]
>>> f
['a', 'c', 'e', 'g']
>>>