Python storing list in class

Question

I'm storing a list in a class in python, but when I later try to access it it's empty. Here is the relevant code and output.

In compiler.py

# globals
verbose = True
current_context = ""

def compile(tokens):
    global verbose, current_context

    if verbose: print("verbose output enabled.")

    # first we want to find all the sections.
    firstpass_token_id = 0
    gathered_tokens = []
    gather_tokens = False
    for t in tokens:
        if gather_tokens:
            gathered_tokens.append(t)

        if t == SECTION:
            current_context = extract_section_name(tokens[firstpass_token_id + 1])
            gather_tokens = True
            if verbose: print("gathering tokens for section", current_context)

        if t == END:
            add_section(current_context, gathered_tokens)
            current_context = ""

            gathered_tokens.clear()
            gather_tokens = False

        firstpass_token_id += 1

    # then we want to call the main section
    call_section("main")

def call_section(name):
    global verbose, current_context

    if verbose: print("calling section", name)

    skip_until_next_end_token = False 

    tokens = get_tokens(name)
    print(len(tokens))

In sections.py

sections = []
section_id = 0

class Section:
    def __init__(self, id, name, tokens):
        self.id = id
        self.name = name

        print("storing the following tokens in", name)
        print(tokens)
        self.tokens = tokens

    def get_tokens(self):
        print("retrieving the following tokens from", self.name)
        print(self.tokens)
        return self.tokens

def add_section(name, tokens):
    global sections, section_id
    sections.append(Section(section_id, name, tokens))
    section_id += 1


def get_tokens(name):
   global sections
   for s in sections:
       if s.name == name:
           return s.get_tokens()

Output

verbose output enabled.
gathering tokens for section foo
storing the following tokens in foo
['foo()', 'var', 'lmao', '=', '2', 'end']
gathering tokens for section main
storing the following tokens in main
['main()', 'var', 'i', '=', '0', 'i', '=', '5', 'var', 'name', '=', '"Douglas"', 'var', 'sentence', '=', '"This is a sentence."', 'foo()', 'end']
calling section main
retrieving the following tokens from main
[]
0

Note that these aren't the complete files, let me know if you need to see more of the code. I'm sure it's something stupid, I haven't worked with python for a couple of months. Thanks.

aghast · Accepted Answer · 2016-02-19 00:13:30Z

1

You are passing in gathered_tokens, so your Section object has self.tokens = tokens.

In other words, gathered_tokens and self.tokens now point to the same list.

Then you call gathered_tokens.clear().

Now they STILL point to the same list. It's an empty list.

Try self.tokens = tokens[:] to make a copy.

answered Feb 19, 2016 at 0:13

aghast

15.4k4 gold badges31 silver badges58 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Python storing list in class

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related