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Apr 17th, 2007

Characters to Lists

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So I'm at the final stages of my program -- it's a working experiment that creates a data file for each participant. My hope was that when I was done, it would be relatively easy to create an analysis program that searches through all the data files and create a nice tab delimited text file that's ready to pop into Excel or SPSS.

However, what I have learned is that, while it's easy to write a list into a string in a file, it's much more difficult to turn it around -- I want to be able to read that same string and turn it right back into a list again. Then I can go through each file, taking the numbers out of the lists written for each participant and putting them all together in one file.

I can't do that if it creates a list character by character, though. Is there some way to maybe mark in the file "this is a list" so that it can be put back together into one later? Or is there another way to store lists of data that I'm not thinking of? Are there any other solutions to my problem?

Right now it looks like I'm going to have to change the way each data file is written to begin with (so that each member of a list is written on a line by itself), then do a lot of copying and pasting -- something of a pain. I would massively appreciate any input on this problem!

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aot

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Apr 17th, 2007

Re: Characters to Lists

is this what you are looking for

Python Syntax (Toggle Plain Text)
>>> s = "this is a string"
>>> alist = list(s)
>>> alist
['t', 'h', 'i', 's', ' ', 'i', 's', ' ', 'a', ' ', 's', 't', 'r', 'i', 'n', 'g']
>>>
>>> s = "this is a string"
>>> alist = list(s)
>>> alist
['t', 'h', 'i', 's', ' ', 'i', 's', ' ', 'a', ' ', 's', 't', 'r', 'i', 'n', 'g']
>>>

ghostdog74

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Apr 17th, 2007

Re: Characters to Lists

No, sorry... I should have been more clear. This is what I want:

Python Syntax (Toggle Plain Text)
list = [1,2,3,4]
write(list)
list = [1,2,3,4]
write(list)

In the file I see:
[1,2,3,4]

I want to be able to get that back as a list. But if I do:

Python Syntax (Toggle Plain Text)
fileHandle = open(file, 'r')
x = fileHandle.readline()
list(x)
print x
fileHandle = open(file, 'r')
x = fileHandle.readline()
list(x)
print x

I get:

Python Syntax (Toggle Plain Text)
['[','1', ',', '2', ',', '3', ',', '4', ']']
['[','1', ',', '2', ',', '3', ',', '4', ']']

I want: [1,2,3,4], a list that I can then use, as in:

Python Syntax (Toggle Plain Text)
 for i in x:
    print i
 
1
2
3
4
 for i in x:
    print i

1
2
3
4

Make more sense now?

aot

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Apr 17th, 2007

Re: Characters to Lists

if in the file, the content is indeed this:

Python Syntax (Toggle Plain Text)
[1,2,3,4]
[1,2,3,4]

then when you read the file line by line, you can use eval() to turn it into a list

Python Syntax (Toggle Plain Text)
for line in open("file"):
    alist =  eval(line)
    #do something with alist.
for line in open("file"):
    alist =  eval(line)
    #do something with alist.

Last edited by ghostdog74; Apr 17th, 2007 at 1:06 pm.

ghostdog74

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Apr 17th, 2007

Re: Characters to Lists

To save and load a whole object like a list, you have to use the module pickle:

python Syntax (Toggle Plain Text)
import pickle
 
myList = [1,2,3,4]
 
# save/dump the list as an object
file = open("myList.dat", "w")
pickle.dump(myList, file)
file.close()
 
# read/load the list as an object
file = open("myList.dat", "r")
myList2 = pickle.load(file)
file.close()
 
# testing
print myList   # [1, 2, 3, 4]
print myList2  # [1, 2, 3, 4]
import pickle
 
myList = [1,2,3,4]
 
# save/dump the list as an object
file = open("myList.dat", "w")
pickle.dump(myList, file)
file.close()
 
# read/load the list as an object
file = open("myList.dat", "r")
myList2 = pickle.load(file)
file.close()
 
# testing
print myList   # [1, 2, 3, 4]
print myList2  # [1, 2, 3, 4]

Lardmeister

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Apr 17th, 2007

Re: Characters to Lists

Ahh, thanks! You guys are the best!!

aot

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