Try this workaround(tested in Firefox and Chrome):
from selenium import webdriver
from selenium.common.exceptions import NoSuchElementException
browser = webdriver.Firefox() # Get local session(use webdriver.Chrome() for chrome)
browser.get("http://www.example.com") # load page from some url
assert "example" in browser.title # assume example.com has string "example" in title
try:
# temporarily make parent(assuming its id is parent_id) visible
browser.execute_script("document.getElementById('parent_id').style.display='block'")
# now the following code won't raise ElementNotVisibleException any more
browser.find_element_by_xpath("//input[@itemcode='XYZ']").send_keys(1)
# hide the parent again
browser.execute_script("document.getElementById('parent_id').style.display='none'")
except NoSuchElementException:
assert 0, "can't find input with XYZ itemcode"
Another workaround is even simpler(assuming the text box's id is "XYZ", otherwise use any JS code that can retrieve it) and probably better if you only want to change the text box's value:
browser.execute_script("document.getElementById('XYZ').value+='1'")