it's all in the documentation:

repo = Repo.clone_from(cloneUrl, localRepopath)
remote = repo.create_remote(remote_name, url=another_url)
remote.push(refspec='{}:{}'.format(local_branch, remote_branch))

see also the push reference API. You can avoid the refspec setting if you set a tracking branch for the remote you want to push to.

Following is the code to git add, git commit and then git push using GitPython.

Install GitPython using pip install gitpython.

from git import Repo

PATH_OF_GIT_REPO = r'path\to\your\project\folder\.git'  # make sure .git folder is properly configured
COMMIT_MESSAGE = 'comment from python script'

def git_push():
    try:
        repo = Repo(PATH_OF_GIT_REPO)
        repo.git.add(update=True)
        repo.index.commit(COMMIT_MESSAGE)
        origin = repo.remote(name='origin')
        origin.push()
    except:
        print('Some error occured while pushing the code')    

git_push()

I'm using gitpython==2.1.11 with Python 3.7. Below is my push function in which I first try a high-level push, and then a low-level push as necessary. Note how I check the return value of either command. I also log the push actions, and this explains what's happening at every step.

class GitCommandError(Exception):
    pass

class Git:
    def _commit_and_push_repo(self) -> None:
        repo = self._repo
        remote = repo.remote()
        remote_name = remote.name
        branch_name = repo.active_branch.name

        # Note: repo.index.entries was observed to also include unpushed files in addition to uncommitted files.
        log.debug('Committing repository index in active branch "%s".', branch_name)
        self._repo.index.commit('')
        log.info('Committed repository index in active branch "%s".', branch_name)

        def _is_pushed(push_info: git.remote.PushInfo) -> bool:
            valid_flags = {push_info.FAST_FORWARD, push_info.NEW_HEAD}  # UP_TO_DATE flag is intentionally skipped.
            return push_info.flags in valid_flags  # This check can require the use of & instead.

        push_desc = f'active branch "{branch_name}" to repository remote "{remote_name}"'
        log.debug('Pushing %s.', push_desc)
        try:
            push_info = remote.push()[0]
        except git.exc.GitCommandError:  # Could be due to no upstream branch.
            log.warning('Failed to push %s. This could be due to no matching upstream branch.', push_desc)
            log.info('Reattempting to push %s using a lower-level command which also sets upstream branch.', push_desc)
            push_output = repo.git.push('--set-upstream', remote_name, branch_name)
            log.info('Push output was: %s', push_output)
            expected_msg = f"Branch '{branch_name}' set up to track remote branch '{branch_name}' from '{remote_name}'."
            if push_output != expected_msg:
                raise RepoPushError(f'Failed to push {push_desc}.')
        else:
            is_pushed = _is_pushed(push_info)
            logger = log.debug if is_pushed else log.warning
            logger('Push flags were %s and message was "%s".', push_info.flags, push_info.summary.strip())
            if not is_pushed:
                log.warning('Failed first attempt at pushing %s. A pull will be performed.', push_desc)
                self._pull_repo()
                log.info('Reattempting to push %s.', push_desc)
                push_info = remote.push()[0]
                is_pushed = _is_pushed(push_info)
                logger = log.debug if is_pushed else log.error
                logger('Push flags were %s and message was "%s".', push_info.flags, push_info.summary.strip())
                if not is_pushed:
                    raise RepoPushError(f'Failed to push {push_desc} despite a pull.')
        log.info('Pushed %s.', push_desc)

Solved it. First created a remote of the other repo

git remote add remote_to_push git@bitbucket...

Then the gitpython code

from git import Repo

repo = Repo('path/to/other/git/repo') #create repo object of the other repository
repo.git.checkout('remote_to_push/master') #checkout to a branch linked to the other repo
file = 'path/to/file' #path to file to push
repo.git.add(file) # same as git add file
repo.git.commit(m = "commit message") # same as git commit -m "commit message"
repo.git.push('remote_to_push', 'HEAD:master') # git push remote_to_push HEAD:master

Aside from the docs, I found the following to be quite helpful if anyone's struggling with gitpython as I found it quite a pain

Python Git Module experiences?

http://sandlininc.com/?p=801

Git push via GitPython

How to push to remote repo with GitPython

I've done something like creating a txt in a remote branch from newly created branch and commit, push to remote. Here's my code

import git
import datetime
import os
from time import *
from os import path
from git import Repo

def commit_files():
    if repo != None:
        new_branch = 'your_new_branch'
        current = repo.create_head(new_branch)
        current.checkout()
        master = self.repo.heads.master
        repo.git.pull('origin', master)
        #creating file
        dtime = strftime('%d-%m-%Y %H:%M:%S', localtime())
        with open(self.local_repo_path + path.sep + 'lastCommit' + '.txt', 'w') as f:
            f.write(str(dtime))
        if not path.exists(self.local_repo_path):
            os.makedirs(self.local_repo_path)
        print('file created---------------------')

        if repo.index.diff(None) or repo.untracked_files:

            repo.git.add(A=True)
            repo.git.commit(m='msg')
            repo.git.push('--set-upstream', 'origin', current)
            print('git push')
        else:
            print('no changes')

I managed this by getting the repo name directly:

 repo = git.Repo('repo_path')
 o = repo.remotes.origin
 o.pull()