Stuck on PHP to Python Translation - php

Question

I'm attempting to translate some PHP code to Python and I'm stuck on the 4th line in the following code (included for context):
$table = array();
for ($i = 0; $i < strlen($text); $i++) {
$char = substr($text, $i, $look_forward);
if (!isset($table[$char])) $table[$char] = array();
}
If array() is used to create an array in PHP, what is $table[$char] = array() doing? Creating a new array inside an existing array? Or is it extending the array?
What is this accomplishing? What would be the Python equivalent to this?
if (!isset($table[$char])) $table[$char] = array();

Answer 1

Seems to me, you should use another data structure than list as table variable. I suppose that dict should be nice for the purpose.
I've just made a quick try to mimic your PHP code in Python:
table = {} # use dictionary instead of list here
for char in text:
if char not in table:
table[char] = []
# do your stuff with table[char]
pass
Also, I suggest you look into https://docs.python.org/3/library/collections.html#collections.defaultdict
With the class the code could be rewritten in the following way:
import collections
table = collections.defaultdict(list)
for char in text:
# do your stuff with table[char], empty list is created by default
pass

Answer 2

if (!isset($table[$char])) $table[$char] = array(); is setting value of $table[$char] variable as array() if $table[$char] is not set yet
$table is empty array, so it has not contain "$char" as key so its checking if $table[$char] is set or not , if not then set its ($table[$char]) value as array().
if you put your code like
$table = array();
for ($i = 0; $i < strlen($text); $i++) {
$char = substr($text, $i, $look_forward);
$table[$char] = array();
}
then it gives notice like Notice: Undefined index: $char in