在 python 中的空 config.txt 文件中读取结果

Question

# read no. of requests
if(os.path.isfile("config.txt")):
        with open("config.txt", "r") as json_file:# Open the file for reading   
            configurations = json.load(json_file) # Read the into the buffer
            # info = json.loads(js.decode("utf-8"))
            print("read config file")
            if("http_requests_count" in configurations.keys()):
                print("present")
                print(configurations["http_requests_count"])
                number_of_requests = int(configurations["http_requests_count"])
                print(number_of_requests)

config.txt file from which i am reading

{
    "first_container_ip": "8100",
    "master_db" : "abc",
    "http_requests_count" : "8",
    "master_name" : "master",
    "slave_names" : ["slave1", "slave2", "slave3"]
}

later in the code, when i am opening the config file to write its giving me error like

io.UnsupportedOperation: not readable

and when i open the config file manually i find it to be empty...

Answer 1

In your full code example, you do

with open("config.txt", "w") as json_file:# Open the file for writing
    configurations = json.load(json_file) # Read the into the buffer

which will fail (can't read from a file opened for writing) and truncate the file (as opening with w does).

This is why you get the UnsupportedOperation error, and why the file ends up being empty.

I suggest refactoring things so you have two simple functions for reading and writing the configuration file:

def read_config():
    if os.path.isfile("config.txt"):
        with open("config.txt", "r") as json_file:
            return json.load(json_file)
    return {}


def save_config(config):
    with open("config.txt", "w") as json_file:
        json.dump(config, json_file)


def scaleup(diff):
    config = read_config()
    slave_name_list = config.get("slave_names", [])
    # ... modify things ...
    config["slave_names"] = some_new_slave_name_list
    save_config(config)


def scaledown(diff):
    config = read_config()
    slave_name_list = config.get("slave_names", [])
    # ... modify things...
    slave_name_list = list(set(slave_name_list) - set(slave_list))
    config["slave_names"] = slave_name_list
    save_config(config)

(As an aside, since you're doing Docker container management, consider using container labels themselves as the master data for your state management instead of a separate file that can easily go out of sync.)