在肯定异常FileNotFoundError之后创建文件

Question

I have written script that parses a web page and saves data of interest in a CSV file. Before I open the data and use it in a second script I check if the file with data exist and if not I am running the parser script first. The odd behaviour of the second script is, that it is able to detect that there is no file, then the file is created, but when it is read for the first time it is empty (part of else statement). I tried to provide some delay by using the time.sleep() method, but it does not work. The explorer clearly shows that the file is not empty, but at the first run, script recognizes the file as empty. At the subsequent runs the scripts clearly sees the file and is able to properly recognize it content.

Maybe You have some explanation for this behaviour.

def open_file():
    # TARGET_DIR and URL are global variables.
    all_lines = []

    try:
        current_file = codecs.open(TARGET_DIR, 'r', 'utf-8')

    except FileNotFoundError:
        procesed_data = parse_site(URL)
        save_parsed(procesed_data)
        compare_parsed()
        open_file()

    else:
        time.sleep(10)
        data = csv.reader(current_file, delimiter=';')

        for row in data:
            all_lines.append(row)
        current_file.close()

        return all_lines

Answer 1

You got some recursion going on.

Another way to do it—assuming I understand correctly—is this:

import os

def open_file():
    # TARGET_DIR and URL are global variables.
    all_lines = []

    # If the file is not there, make it.
    if not os.path.isfile(TARGET_DIR):
        procesed_data = parse_site(URL)
        save_parsed(procesed_data)
        compare_parsed()
        # Here I am assuming the file has been created.

    current_file = codecs.open(TARGET_DIR, 'r', 'utf-8')
    data = csv.reader(current_file, delimiter=';')
    for row in data:
        all_lines.append(row)
    current_file.close()
    return all_lines

Answer 2

you should return the result of your internal open_file call, or just opening the file in your except block:

def open_file():
    # TARGET_DIR and URL are hopefully constants
    try:
        current_file = codecs.open(TARGET_DIR, 'r', 'utf-8')
    except FileNotFoundError:
        procesed_data = parse_site(URL)
        save_parsed(procesed_data)
        compare_parsed()
        current_file = codecs.open(TARGET_DIR, 'r', 'utf-8')

    data = csv.reader(current_file, delimiter=';')
    all_lines = list(data)
    current_file.close()
    return all_lines