Question

I am iterating through a database and want to add the variable value of key “number” to a list x, only if this key exists. There are some documents where there is no key “number”.

Inside mongo I would use the $exist, but I don’t know how to do it in python. I tried this but it doesn’t work…

for i in database:
    try:
        x.append(i["number"])
    except NameError:
        break

This doesn’t work, and I am sure there is a more elegant way…

Answer 1

The in operator is the canonical way to test existence of a key in a container:

for i in database:
    if "number" in i:
        x.append(i["number"])