Update: thanks to the comments I changed the code the following way (it's not finished yet).

cmd_parameter_user = "config1.cfg"
cmd_parameter_global = "global.cfg"

config_file_user = []
config_file_global = []

conf_key_split1 = '.'
conf_key_split2 = '='
conf_key_split3 = ','

dict_config_user = {}
dict_config_global = {}
dict_config = {}

if len(sys.argv) == 2:
    cmd_parameter_user = sys.argv[1]
else:
    print("Error: there should be only one argument after program name - config file name")
    exit(-1)

def read_file(filename, message):
# function for reading from file to list of lines
    try:
        with open(filename) as file_:
            return file_.readlines()
    except FileNotFoundError:
        print(message.format(filename))
        exit(-1)

# reading user's and global config files
config_file_user = read_file(cmd_parameter_user, "File '{}' not exists or not available")
config_file_global = read_file(cmd_parameter_global, "File '{}' not exists or not available")


def parse_list(filename, dictname):
# function for parsing list of lines into a dict
    for line in filename:
        if line.startswith(conf_key_split1):
            line = line.rstrip().split(conf_key_split1)
            line = line[1]

            (key, val) = line.split(conf_key_split2)
            dictname.update({key: val})

# parsing user's and global config files
parse_list(config_file_user, dict_config_user)
parse_list(config_file_global, dict_config_global)


def update_dicts(dictname1, dictname2):
# function for updating (merging) dicts
    dictname1.update(dictname2)
    return dictname1


def value_from_dict(param):
# function for searching the value of param in dict
    if param in dict_config:
        return dict_config.get(param)
    else:
        print('The value of the parameter "', param, '" was not found in either', cmd_parameter_global, 'or', cmd_parameter_user)
        exit(-1)

dict_config = update_dicts(dict_config_global, dict_config_user)

Usage:

names = int(value_from_dict('names'))

Update: thanks to the comments I changed the code the following way (it's not finished yet).

cmd_parameter_user = "config1.cfg"
cmd_parameter_global = "global.cfg"

config_file_user = []
config_file_global = []

conf_key_split1 = '.'
conf_key_split2 = '='
conf_key_split3 = ','

dict_config_user = {}
dict_config_global = {}
dict_config = {}

if len(sys.argv) == 2:
    cmd_parameter_user = sys.argv[1]
else:
    print("Error: there should be only one argument after program name - config file name")
    exit(-1)

def read_file(filename, message):
# function for reading from file to list of lines
    try:
        with open(filename) as file_:
            return file_.readlines()
    except FileNotFoundError:
        print(message.format(filename))
        exit(-1)

# reading user's and global config files
config_file_user = read_file(cmd_parameter_user, "File '{}' not exists or not available")
config_file_global = read_file(cmd_parameter_global, "File '{}' not exists or not available")


def parse_list(filename, dictname):
# function for parsing list of lines into a dict
    for line in filename:
        if line.startswith(conf_key_split1):
            line = line.rstrip().split(conf_key_split1)
            line = line[1]

            (key, val) = line.split(conf_key_split2)
            dictname.update({key: val})

# parsing user's and global config files
parse_list(config_file_user, dict_config_user)
parse_list(config_file_global, dict_config_global)


def update_dicts(dictname1, dictname2):
# function for updating (merging) dicts
    dictname1.update(dictname2)
    return dictname1


def value_from_dict(param):
# function for searching the value of param in dict
    if param in dict_config:
        return dict_config.get(param)
    else:
        print('The value of the parameter "', param, '" was not found in either', cmd_parameter_global, 'or', cmd_parameter_user)
        exit(-1)

dict_config = update_dicts(dict_config_global, dict_config_user)

Usage:

names = int(value_from_dict('names'))

Firstly I wrote a function but then I needed a class. It's my first working class in Python, and I ask if you can kindly note its defects. Although it works, I think it can for sure be written more correctly and concisely. Thanks beforehand.

Firstly I wrote a function but then I needed a class. It's my first working class in Python, and I ask if you can kindly note its defects. Although it works, I think it can for sure be written more correctly and concisely.