Passing a variable in URL?

I'm new in Python. I have a file which has a bunch of ids (integer values) written in them. It's a text file.

Now I need to pass each id inside the file into a url.

For example "https://example.com/[id]"

It will be done in this way

A = json.load(urllib.urlopen("https://example.com/(the first id present in the text file)"))
print A

What this will essentially do is that it will read certain information about the id present in the above URL and display it. I want this to work in a loop format where in it will read all the ids inside the text file and pass it to the URL mentioned in 'A' and display the values continuously..is there a way to do this?

Old style string concatenation can be used

>>> id = "3333333"
>>> url = "https://example.com/%s" % id
>>> print url
https://example.com/3333333
>>> 

The new style string formatting:

>>> url = "https://example.com/{0}".format(id)
>>> print url
https://example.com/3333333
>>> 

The reading for file as mentioned by avasal with a small change:

f = open('file.txt', 'r')
for line in f.readlines():
    id = line.strip('\n')
    url = "https://example.com/{0}".format(id)
    urlobj = urllib.urlopen(url)
    try:
        json_data = json.loads(urlobj)
        print json_data
    except:
        print urlobj.readlines()