Question

I’m trying to solve this newbie puzzle:

I’ve created this function:

def bucket_loop(htable, key):
    bucket = hashtable_get_bucket(htable, key)
    for entry in bucket:
        if entry[0] == key:          
            return entry[1]                         
    return None

And I have to call it in two other functions (bellow) in the following way: to change the value of the element entry[1] or to append to this list (entry) a new element. But I can’t do that calling the function bucket_loop the way I did because “you can’t assign to function call” (assigning to a function call is illegal in Python). What is the alternative (most similar to the code I wrote) to do this (bucket_loop(htable, key) = value and hashtable_get_bucket(htable, key).append([key, value]))?

def hashtable_update(htable, key, value):
    if bucket_loop(htable, key) != None:
        bucket_loop(htable, key) = value
    else:
        hashtable_get_bucket(htable, key).append([key, value])

def hashtable_lookup(htable, key):
    return bucket_loop(htable, key)

Thanks, in advance, for any help!

This is the rest of the code to make this script works:

def make_hashtable(size):
    table = []
    for unused in range(0, size):
        table.append([])
    return table

def hash_string(s, size):
    h = 0
    for c in s:
         h = h + ord(c)
    return h % size

def hashtable_get_bucket(htable, key):
    return htable[hash_string(key, len(htable))]

Similar question (but didn’t help me): SyntaxError: "can't assign to function call"

Answer 1

In general, there are three things you can do:

1. Write “setter” functions (ex, bucket_set)
2. Return mutable values (ex, bucket_get(table, key).append(42) if the value is a list)
3. Use a class which overrides __getitem__ and __setitem__

For example, you could have a class like like:

class Bucket(object):
    def __setitem__(self, key, value):
        # … implementation …
    def __getitem__(self, key):
        # … implementation …
        return value

Then use it like this:

>>> b = Bucket()
>>> b["foo"] = 42
>>> b["foo"]
42
>>> 

This would be the most Pythonic way to do it.