Daniel'strae - Filed under 'PHP'

Best way to retrieve variable values from a text file - Python - Json

Referring on this question, i have a similar -but not the same- problem..

On my way, i'll have some text file, structured like:

var_a: 'home'
var_b: 'car'

var_c: 15.5

And i need that python read the file and then create a variable named var_a with value 'home', and so on.

Example:

#python stuff over here
getVarFromFile(filename) #this is the function that im lookin for

print var_b
#output: car, as string
print var_c
#output 15.5, as number.

Is this possible, i mean, even keep the var type?

Notice that i have the full freedom to the text file structure, i can use the format i like if the one i proposed isn't the best.

EDIT: the ConfigParser can be a solution, but i dont like it so much, becose in my script i'll have then to refer to the variables in the file with

config.get("set", "var_name")

But what i'll love is to refer to the variable direclty, as i declared it in the python script..

There is a way to impoer the file as a python dictionary?

Oh, last thing, keep in mind that i dont know exactly how many variables would i have in the text file

Edit 2: i'm very interessing to the stephan json solution, becose in that way the text file could be readed simply with others languages (php, then via ajax javascript, for example), but i fail in something while acting that solution:

#for the example, i dont load the file but create a var with the supposed file content
file_content = "'var_a': 4, 'var_b': 'a string'"

mydict = dict(file_content)
#Error: ValueError: dictionary update sequence element #0 has length 1; 2 is required

file_content_2 = "{'var_a': 4, 'var_b': 'a string'}"
mydict_2 = dict(json.dump(file_content_2, True))

#Error:
#Traceback (most recent call last):
#File "<pyshell#5>", line 1, in <module>

#mydict_2 = dict(json.dump(file_content_2, True))
#File "C:\Python26\lib\json\__init__.py", line 181, in dump

#fp.write(chunk)
#AttributeError: 'bool' object has no attribute 'write'

In what kind of issues can i fall with the Json format? And, how can i read a json array in a text file, and transform it in a python dict?

p.s: i dont like the solution using .py files, i'll prefer .txt, .inc, .whatever is not restrictive to one language

python textfiles variables json

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edited May 29 at 10:01

asked May 29 at 6:48

DaNieL
418●9

You can't manage without any import modules... you could manage with just the sys module, but it wouldn't be as nice as the other solutions suggested :) – workmad3 May 29 at 7:12

ok, its not a big problem – DaNieL May 29 at 7:16

regarding your Edit2: you want the_dict = json.loads('{"var_a": 4, "var_b": "a string"}'). Pls note that I have switched " and '. – stephan May 29 at 9:13

And that's exactly what i want. Thanks man! – DaNieL May 29 at 9:33

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6 Answers

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Load your file with JSON or PyYAML into a dictionary the_dict (see doc for JSON or PyYAML for this step, both can store data type) and add the dictionary to your globals dictionary, e.g. using globals().update(the_dict).

If you want it in a local dictionary instead (e.g. inside a function), you can do it like this:

for x in the_dict.items():

    exec('%s=%s' % x)

as long as it is safe to use exec. If not, you can use the dictionary directly.

link

edited May 29 at 10:32

answered May 29 at 7:42

stephan
500●7

Can you please show a basilar example? – DaNieL May 29 at 7:58

1

A shorter idiom is globals().update(the_dict) or locals().update(the_dict). – Jouni K. Seppänen May 29 at 10:12

Thanks for pointing this out for globals(). Amended my answer. locals() is however read-only (see docs.python.org/library/functions.html#locals/…). – stephan May 29 at 10:29

It's not really read-only (I have used it myself) but apparently there are circumstances in which writing to it doesn't work. Thanks for pointing this out. – Jouni K. Seppänen May 31 at 9:59

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But what i'll love is to refer to the variable direclty, as i declared it in the python script..

Assuming you're happy to change your syntax slightly, just use python and import the "config" module.

# myconfig.py:

var_a = 'home'

var_b = 'car'
var_c = 15.5

Then do

from myconfig import *

And you can reference them by name in your current context.

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answered May 29 at 7:54

yangyang
96●3

+1, This is absolutely THE best way to do config files. No need to grow your own config syntax, config parsers, config loaders etc. when you can just re-use python's core parts! – Simon May 29 at 8:13

+1 yes, as long as you can trust your config file and don't need portability – stephan May 29 at 8:26

Convenience and flexibility ++ vs. security -- : in some situations it's great, in others... less so. – mavnn May 29 at 8:28

I have to discard this solution becose i dont want to restric the file to python only, i think is better to use a generic file format (.txt, .inc, .whatever) that can be accessed by others languages too (with all the safe measure that this solution will mean). Anyway i'll keep in mind this way for the future – DaNieL May 29 at 9:37

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Use ConfigParser.

Your config:

[myvars]
var_a: 'home'

var_b: 'car'
var_c: 15.5

Your python code:

import ConfigParser

config = ConfigParser.ConfigParser()

config.read("config.ini")
var_a = config.get("myvars", "var_a")

var_b = config.get("myvars", "var_b")

var_c = config.get("myvars", "var_c")

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edited May 29 at 8:25

answered May 29 at 6:57

Igor Krivokon
1,393●9

Just edited - this way is fine, but if possible im lookin for another one who would let me using the variables in a usefull way – DaNieL May 29 at 7:17

I've updated the answer to show you how to use these as variables. – Igor Krivokon May 29 at 8:26

Or you could take the Bunch class from code.activestate.com/recipes/52308/ and hack it to be recursive, so you could refer to config.myvars.var_a directly. – Jouni K. Seppänen May 29 at 10:16

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How reliable is your format? If the seperator is always exactly ': ', the following works. If not, a comparatively simple regex should do the job.

As long as you're working with fairly simple variable types, Python's eval function makes persisting variables to files surprisingly easy.

(The below gives you a dictionary, btw, which you mentioned was one of your prefered solutions).

def read_config(filename):
    f = open(filename)

    config_dict = {}
    for lines in f:

        items = lines.split(': ', 1)

        config_dict[items[0]] = eval(items[1])

    return config_dict

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edited May 29 at 10:48

answered May 29 at 8:27

mavnn
312●9

I can wrote the text file exaclty as i want, the format var: value is just for example, if others formats are better, fell free to suggest – DaNieL May 29 at 8:37

As long as it's consistant, and the value is of the form generated by repr(variable) it doesn't really matter for this method. Just pick a seperator that will never be part of the variable name and use that in the split method. – mavnn May 29 at 10:47

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What you want appear to want is the following, but this is NOT RECOMMENDED:

>>> for line in open('dangerous.txt'):

...     exec('%s = %s' % tuple(line.split(':', 1)))

... 
>>> var_a
'home'

This creates somewhat similar behavior to PHP's register_globals and hence has the same security issues. Additionally, the use of exec that I showed allows arbitrary code execution. Only use this if you are absolutely sure that the contents of the text file can be trusted under all circumstances.

You should really consider binding the variables not to the local scope, but to an object, and use a library that parses the file contents such that no code is executed. So: go with any of the other solutions provided here.

(Please note: I added this answer not as a solution, but as an explicit non-solution.)

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answered May 29 at 7:55

Stephan202

community wiki

Yes, thanks for the raccomandation, i've banned the exec function both from my php and python scripts time ago ;) – DaNieL May 29 at 7:59

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0	You can treat your text file as a python module and load it dynamically: `import`

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Daniel’strae

Is cuma cá mhinice a théann tú ar strae; is é is tábhachtaí gurb áil leat do bhealach a aimsiú arís.

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Best way to retrieve variable values from a text file - Python - Json

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