How to escape charachters in a Python string while reading it as an environment variable using ConfigParser

Question

I am getting the following error--- "configparser.InterpolationSyntaxError: '%' must be followed by '%' or '(', found: '%dCUD'"

I want to read credentials which are set as an environment variables as well as present in .config file. So I am using pythons ConfigParser as follows.

import configparser as cp
from configparser import ConfigParser
config = ConfigParser(os.environ)    #<-- this enables ConfigParser to read from environment variable
config.read(CONFIG_FILEPATH)       #<--- this is to read from .confog file


My .config file is like this--
[Postgres]
Postgres.host = XXX.com
Postgres.METADATADB=pda-study-beta
Postgres.DATAREFRESHDB=
Postgres.user= %(XXXX)s
Postgres.password = %(Postgres_Pass)s

anything included inside *%()s* means it is being read from environment variable. 

I read it in my scripts as follows:
config.get('Postgres','Postgres.password')


It works fine for all but for password, its throwing me following error in password section--
"configparser.InterpolationSyntaxError: '%' must be followed by '%' or '(', found: '%dCUD'"

Its because my password contains '%' character. e.g.(xxx%dCUDxx)

Does any one have any idea how do I handle this. We can escape % with another %, but in my case, I am reading password from environment variable, so cant manipulate it. 

Can anyone please help me resolve this ?

Kurtis Rader · Accepted Answer · 2020-06-04 23:39:18Z

1

The configparser module documentation is ambiguous but if you look at the source code you can see, in method _interpolate_some, that % expansion is recursive. That is, % expansion is also done to the interpolated value -- the password in your example.

I am reading password from environment variable, so cant manipulate it.

It's true you probably don't want to mutate the global env vars. But nothing stops you from making a copy and mutating that copy. For example,

config = ConfigParser({k: v.replace('%', '%%') for k, v in os.environ.items()})

answered Jun 4, 2020 at 23:39

Kurtis Rader

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1 Comment

Vikas Garud Over a year ago

Thanks Kurtis Rader.

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