A problem with list

[export]

The following code
##############
import string
MyList=['abc','def']
for i in MyList:
print i
###############

works as I expect that is I get
abc
def

but when I have Mylist in a file and I read it from the file it does
not work as I expect.
#########
import string
ff=open('C:\\Robotp\\MyFile.txt','r') # read MyList from a file
MyList=ff.read()
for i in MyList:
print i
###########
I will get
[
'
a
b
c
'
,
'
d
e
f
'
]

where my MyFile.txt looks like this:
['abc','def']

Where is a problem?
Thanks for help
Lad

 

[gawel]

The following code
##############
import string
MyList=['abc','def']
for i in MyList:
print i
###############

works as I expect that is I get
abc
def

but when I have Mylist in a file and I read it from the file it does
not work as I expect.
#########
import string
ff=open('C:\\Robotp\\MyFile.txt','r') # read MyList from a file
MyList=ff.read()
for i in MyList:
print i
###########
I will get
[
'
a
b
c
'
,
'
d
e
f
'
]

where my MyFile.txt looks like this:
['abc','def']

Where is a problem?
Thanks for help
Lad

That's quite simple. Your file contain a string, not a list
You must use eval(your_list_as_string).

>>> f = open('/tmp/list')
>>> f.seek(0)
>>> s = f.read()
>>> s "['adc','def']\n"
>>> l = eval(s)
>>> l ['adc', 'def']
>>> for i in l:

.... print i
....
adc
def

gawel

 

[Roy Smith]

but when I have Mylist in a file and I read it from the file it does
not work as I expect.
#########
import string
ff=open('C:\\Robotp\\MyFile.txt','r') # read MyList from a file
MyList=ff.read()
for i in MyList:
print i
###########
I will get
[
'
a
b
c
'
,
'
d
e
f
'
]

where my MyFile.txt looks like this:
['abc','def']

The problem is that read() just reads in characters of text and stores
them in a string. It doesn't *execute* that text as if it were a
program. You want to do one of two things. The first, which requires
no changes to your file, would be to eval the text you read. For
example:

s = "['foo', 'bar']"
s "['foo', 'bar']"
type (s)

<type 'str'>

s is a string containing the printed representation of a list. You
turn that into a real list by passing the string to eval()

l = eval (s)
l ['foo', 'bar']
type (l)

<type 'list'>

Alternatively (and probably the direction you want to be looking), is
to alter your file a little and import it. Make your file look like:

x = ['abc', 'def']

Assuming the filename is "foo.py", you can do "import foo" and your
file will be read AND EXECUTED, and a module will be created with the
same name as the basename of the file. The variable x will be a
variable inside that module:
['abc', 'def']

 

[Fuzzyman]

An alternative is reading the list into a string and using my
'listquote' module. It will tun strings into lists (and vice versa) -
including nested lists (lists of lists) and properly handling quoted
elements.

http://www.voidspace.org.uk/atlantibots/pythonutils.html

It won't do integer conversions though - only strings.

Regards,

Fuzzy

 

[Jeff Shannon]

That's quite simple. Your file contain a string, not a list
You must use eval(your_list_as_string).

....except that eval() is a huge security hole. A better bet would be to
use either the listquote module mentioned elsewhere, or to find an
alternative way of storing your data that *doesn't* require using eval()
to read it back in from disk. One possibility would be the ConfigParser
module, which makes it easy to store (and retrieve) information from
..ini-style files and/or the Windows Registry.

Jeff Shannon
Technician/Programmer
Credit International