Python recursion return differs

Question

The return of a python recusion differs and I do not understand why:

from bs4 import BeautifulSoup


def recurse_table(table, table_list):
    if table.find_next("table") is not None:
        recurse_table(table.find_next("table"), table_list)
    table_list.append(table)
    return table_list


fp = open("tc4400_cs_2.html")
soup = BeautifulSoup(fp.read(), features="html.parser")
print(len(recurse_table(soup.find("table"), [])))

returns correct length (4).

Whereas

from bs4 import BeautifulSoup


def recurse_table(table, table_list):
    if table.find_next("table") is not None:
        recurse_table(table.find_next("table"), table_list)
    return table_list.append(table)


fp = open("tc4400_cs_2.html")
soup = BeautifulSoup(fp.read(), features="html.parser")
print(len(recurse_table(soup.find("table"), [])))

returns TypeError: object of type 'NoneType' has no len()

What am I missing?

Shinra tensei · Accepted Answer · 2020-04-15 10:24:52Z

1

The return differs because what you're returning differs. The .append() method modifies table_list but does not return it, instead it returns a None. If you want to return the list, then you should append table to the list in one line and then in the next return the list, just like you already do in the first code.

edited Apr 15, 2020 at 10:24

answered Apr 15, 2020 at 10:19

Shinra tensei

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