Overriding library functions in Python

What you want to do is as the title says, so you can skip the introduction.

Background, introduction

I was writing an app to play with Google Calendar using the Google API Client Library. Drop the OAuth2 client information from Google Cloud Platform as client_secret.json and specify the ** file name ** in the argument of ʻoauth2client.client.flow_from_clientsecrets ()`.

The problem here. I don't want to add client_secret.json to git version control due to security concerns. However, I'm running the app on Heroku, so I can't upload files. (It seems that you should use object storage such as Amazon S3, but I stopped it because it is annoying because I have never used it)

So I had to specify client_secret.json, but I was having trouble putting that file on the Heroku server.

So, I want to put dictionary type data in ʻoauth2client.client.flow_from_clientsecrets () function instead of file name. Then, store the contents of client_secret.json` in the environment variables of Heroku and put them in the dictionary data. (Is it really bad to put confidential information in environment variables?)

Postscript

After writing the code, I realized that I should have created an instance of ʻOAuth2WebServerFlow` normally. Therefore, it is not necessary to override it separately, but I will leave it because I learned that it can be overridden in this way.

Thing you want to do

ʻOauth2client.client.flow_from_clientsecrets ()` I want the function to contain ** dictionary type ** instead of ** filename **.

What happened

The source code of the library looked like this. (The following is an excerpt from the Apache license code of Google Inc.)

Partially omitted from ʻoauth2client.client.py`.

@_helpers.positional(2)
def flow_from_clientsecrets(filename, scope, redirect_uri=None,
                            message=None, cache=None, login_hint=None,
                            device_uri=None, pkce=None, code_verifier=None):
    try:
        client_type, client_info = clientsecrets.loadfile(filename,
                                                          cache=cache)
        if client_type in (clientsecrets.TYPE_WEB,
        -----The following is omitted------

Note that filename is passed toclientsecrets.loadfile (). I also looked at clientsecrets.loadfile ().

def loadfile(filename, cache=None):
    _SECRET_NAMESPACE = 'oauth2client:secrets#ns'

    if not cache:
        return _loadfile(filename)

    obj = cache.get(filename, namespace=_SECRET_NAMESPACE)
    -----The following is omitted------

If cache does not exist, the processing is transferred to the _loadfile function. Let's take a look at _loadfile.

def _loadfile(filename):
    try:
        with open(filename, 'r') as fp:
            obj = json.load(fp)
    except IOError as exc:
        raise InvalidClientSecretsError('Error opening file', exc.filename,
                                        exc.strerror, exc.errno)
    return _validate_clientsecrets(obj)

I arrived at the function that is loading the file. If you override this function, you might put a dictionary type in the filename argument.

So after that my code

# `client.flow_from_clientsecrets`Functions can take dictionary type as arguments
# `clientsecrets._loadfile`Override function
def new_loadfile(data):
    return clientsecrets._validate_clientsecrets(data)
clientsecrets._loadfile = new_loadfile

After this

flow = client.flow_from_clientsecrets(
Dictionary type,
    scope='https://www.googleapis.com/auth/calendar',
    redirect_uri=flask.url_for('oauth2callback', _external=True))

You can now use flow_from_clientsecrets, which takes a dictionary type as an argument.

Summary

def new_func(args):
    #Various processing
    return hoge
hoge_library.func = new_func

This way it's easy to override and it affects all the functions that use that function.

Overriding library functions I did it for the first time, but it works so easily. I'm scared.