Read page source before POST

I want to know if there is a way to POST parameters after reading the page source. Ex: read captcha before posting ID#

My current code:

import requests
id_number = "1"
url = "http://www.submitmyforum.com/page.php"
data = dict(id = id_number, name = 'Alex')
post = requests.post(url, data=data)

There is a captcha that is changeable after every request to http://submitforum.com/page.php (obv not a real site) I would like to read that parameter and submit it to the "data" variable.

As discussed in OP comments, selenium can be used, methods without browser emulation may also exists !

Using Selenium (http://selenium-python.readthedocs.io/) instead of requests module method:

import re
import selenium
from selenium import webdriver

regexCaptcha = "k=.*&co="
url = "http://submitforum.com/page.php"

# Get to the URL
browser = webdriver.Chrome()
browser.get(url)

# Example for getting page elements (using css seletors)
# In this example, I'm getting the google recaptcha ID if present on the current page
try:
    element = browser.find_element_by_css_selector('iframe[src*="https://www.google.com/recaptcha/api2/anchor?k"]')
    captchaID = re.findall(regexCaptcha, element.get_attribute("src"))[0].replace("k=", "").replace("&co=", "")
    captchaFound = True
    print "Captcha found !", captchaID
except Exception, ex:
    print "No captcha found !"
    captchaFound = False

# Treat captcha
# --> Your treatment code

# Enter Captcha Response on page
captchResponse = browser.find_element_by_id('captcha-response')
captchResponse.send_keys(captcha_answer)

# Validate the form
validateButton = browser.find_element_by_id('submitButton')
validateButton.click()

# --> Analysis of returned page if needed