CODEWITHSUNDEEP
pythonvariablestext
Paolo
Paolo

Reputation: 2229

Using a text file to receive a string for a variable in Python, without defining it

I have a text file in which there are several variables. Most of them are used in a Bash script of mine, but I'd like to use the same text file for my Python script. For the lines that are not properly formatted for Python, I want my script to just ignore. For those that are properly formatted, I want the script to check and if it's the variable I'm looking for - use it.

import sys import re

for ln in open("thefile.txt"):
        m = re.match(r"(?P<varname>[^=]*)\s*=\s*(?P<value>.+)", ln)
        if m:
                varname = m.group("varname")
                value_string = m.group("value")
                value = eval(value_string)
                print value
                # so if the variables name is THISVARIABLE, get that value:
                if varname == "THISVARIABLE":
                        mypythonvariable == value

I'm getting the following error:

NameError: name 'Somevariableinmytextfile' is not defined

The Somevariableinmytextfile is the first variable in that file.

My question:

Do I have to define every variable in the txt file, in order to get rid of this error? If not, what shall I do? I'm very new at Python. This is my first program.

Upvotes: 2

Views: 571

Answers (3)

michaelb958--GoFundMonica
michaelb958--GoFundMonica

Reputation: 4708

The error is eval complaining that the contents of value_string have no meaning as a whatever-it-is.

The real error is using eval at all. (A good post on the pitfalls can be found here.) You don't even need to eval here - leaving value_string as the string the regex gave you will be just fine.

The problem with the present approach

Sample thefile.txt:

foo=bar
baz=42
quux=import os; os.shutdown()
  • When parsing foo, Python complains that bar isn't defined. (Simple.)
  • When parsing bar, Python gives you an int instead of a str. (No real problem...)
  • When parsing quux, Python shuts down your computer. (Uh oh!)

Why you don't need eval

You want a string value, correct? The regex already gives you a string!

varname = m.group("varname")
value = m.group("value")
print value
if varname == "THISVARIABLE":
    mypythonvariable = value # You meant = instead of ==?

Upvotes: 1

P0W
P0W

Reputation: 47784

eval throws the error, the value_string's value (which should be a variable) needs to be defined before use.

Upvotes: 0

nio
nio

Reputation: 5289

You get the error because a line in your thefile.txt file:

TEST = ABC

will be evaluated in python as TEST will be assigned to a value of variable ABC but you have no ABC defined.

You could make a dictionary to store your value pairs... this will work with string values:

variables = {}
accepted = ['THISVARIABLE', 'ANOTHERONE']
...
if varname in accepted:
    variables[varname]=value

Upvotes: 0

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