newbie question: how to read back the dictionary from a file?

[lancered]

Hi Dear all,

I have some data here in the form of a dictionary, called "vdic". Then
I write them to a data file "f" using the write function as
f.write(str(vdic)). The keys of this dictionary are integers and
values are float numbers. Something like this:

{ 1: 0.00951486513347, 2: 0.0388123556019, ... ...}

Now, I want to read these data back in another function. Of course, I
could parse the string little by little, e.g, first read a "{", then
loop read a int, then read a ":", then a float etc etc... Since it is
written out with standard python builtin functions, I guess there may
be some more direct method than this, say a function in some modules?
Could someone give me a hint?

 

[7stud]

Hi Dear all,

I have some data here in the form of a dictionary, called "vdic". Then
I write them to a data file "f" using the write function as
f.write(str(vdic)). The keys of this dictionary are integers and
values are float numbers. Something like this:

{ 1: 0.00951486513347, 2: 0.0388123556019, ... ...}

Now, I want to read these data back in another function. Of course, I
could parse the string little by little, e.g, first read a "{", then
loop read a int, then read a ":", then a float etc etc... Since it is
written out with standard python builtin functions, I guess there may
be some more direct method than this, say a function in some modules?
Could someone give me a hint?

Try:

import shelve

s = shelve.open("newFile.dat")
s["d"] = {"red":2, 3:"blue", 2.5:"x"}
s.close()

s = shelve.open("newFile.dat")
print s["d"]
my_dict = s["d"]
print my_dict[2.5]

 

[Amit Khemka]

Hi Dear all,

I have some data here in the form of a dictionary, called "vdic". Then
I write them to a data file "f" using the write function as
f.write(str(vdic)). The keys of this dictionary are integers and
values are float numbers. Something like this:

{ 1: 0.00951486513347, 2: 0.0388123556019, ... ...}

Now, I want to read these data back in another function. Of course, I
could parse the string little by little, e.g, first read a "{", then
loop read a int, then read a ":", then a float etc etc... Since it is
written out with standard python builtin functions, I guess there may
be some more direct method than this, say a function in some modules?
Could someone give me a hint?

Check out cPickle or shelve modules.

Cheers,
--

 

[7stud]

s.close()

 

[Fuzzyman]

Hi Dear all,

I have some data here in the form of a dictionary, called "vdic". Then
I write them to a data file "f" using the write function as
f.write(str(vdic)). The keys of this dictionary are integers and
values are float numbers. Something like this:

{ 1: 0.00951486513347, 2: 0.0388123556019, ... ...}

Now, I want to read these data back in another function. Of course, I
could parse the string little by little, e.g, first read a "{", then
loop read a int, then read a ":", then a float etc etc... Since it is
written out with standard python builtin functions, I guess there may
be some more direct method than this, say a function in some modules?
Could someone give me a hint?

ConfigObj and its 'unrepr' mode gives you a useful (and simple) way of
preserving and restoring basic Python datatypes.

The file format is a very readable 'ini' format - and the basic
interface is like a dictionary, for both writing and retrieving
values.

http://www.voidspace.org.uk/python/configobj.html

Fuzzyman

 

[Alex Martelli]

Hi Dear all,

I have some data here in the form of a dictionary, called "vdic". Then
I write them to a data file "f" using the write function as
f.write(str(vdic)). The keys of this dictionary are integers and
values are float numbers. Something like this:

{ 1: 0.00951486513347, 2: 0.0388123556019, ... ...}

Now, I want to read these data back in another function. Of course, I
could parse the string little by little, e.g, first read a "{", then
loop read a int, then read a ":", then a float etc etc... Since it is
written out with standard python builtin functions, I guess there may
be some more direct method than this, say a function in some modules?
Could someone give me a hint?

Others have suggested better ways of writing the file out. However,
it's possible to recover the data from the string form you've written,
via the eval builtin function -- with all sorts of caveats (won't be as
fast as other approaches, enormous security risk if anybody could have
tampered with the file, etc).

To mitigate the security risks a little, try

eval(thestr, dict(__builtins__={}))

or more advanced approaches such as discussed at
<http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/364469>,
<http://mail.python.org/pipermail/python-list/2006-June/390979.html>
etc.


Alex