Month: June 2014

Parsing Dict object from text file (Updates)

I have been using the DictParser created as mentioned in previous blog in a recent project to create a setting file for various users. In the project, different users need to have different settings such as parameter filepath.

The setting file created will use the computer name to segregate the different users. By creating a text file (with Dict Parser) based on the different computer names, it is easy to get separate setting parameters for different users. Sample of the setting file are as below.

## Text file

## end of file

The output from DictParser are as followed:

## python output as one dict containing two dicts with different user'USER1_COM_NAME' and 'USER2_COM_NAME'
>> {'USER1_COM_NAME': {'setting2': ['c:\\data\\temp\\ccc.txt']}, 'USER2_COM_NAME': {2: [1, 'bbb', 'cccc', 1, 2, 3], 'setting': ['c:\\data\\temp\\eee.txt']}}

User can use the command “os.environ[‘ComputerName’]” to get the corresponding setting filepath.

I realized that the output format is somewhat similar to json format. This parser is more restrictive in uses hence has some advantage over json in less punctuations (‘{‘, ‘\’) etc and able to comment out certain lines.

Parsing dict object from text file

Sometimes we need to store the different settings in a text file. Getting the different configurations will be easier if each particular setting group is a dict with the different key value pairs. The dict objects can be passed to other functions or modules with ease.

I created the following script that is able to parse the strings from a text file as separate dict obj with base type. This allows user to create the dict object easily in a text file. As for now, the values the dict can take basic type such as int, float and string.

Creating the text file format is simple. Starting a dict on a new line with $ <dict name>  followed by the key value pairs in each subsequent line. The format for the pair is <key>:<value1,value2…>

Example of a file format used is as below:

## Text file

## end of file
## python output as one dict containing two dicts with name 'first' and 'second'
>> {'first': {'aa':['bbb','cccc',1,2,3],1:[1,'bbb','cccc',1,2,3]},
   'second': {'ee':['bbb','cccc',1,2,3],2:[1,'bbb','cccc',1,2,3]}}

The script is relatively simple, making use of the literal_eval method in ast module to convert the string to various base type. It does not have the danger of eval() method. Below is the code for the method for string conversion.

    def convert_str_to_correct_type(self, target_str):
        """ Method to convert the str repr to the correct type
            Idea from
                target_str (str): str repr of the type

                (str/float/int) : return the correct representation of the type

            return ast.literal_eval(target_str)
        except ValueError:
            ## not converting as it is string
        return target_str

The rest of script is the reading of the different line and parsing it with correct info. The method can be summarized as below method call.

    def parse_the_full_dict(self):
        """Method to parse the full file of dict
            Once detect dict name open the all the key value pairs


        self.dict_of_dict_obj = {}
        ## start parsing each line
        ## intialise temp_dict obj
        start_dict_name = ''
        for line in self.filedata:
            if self.is_line_dict_name(line):
                start_dict_name = self.parse_dict_name(line)
                ## intialize the object
                self.dict_of_dict_obj[start_dict_name] = dict()

            elif self.is_line_key(line):

                 temp_key, temp_value = self.parse_key(line)
                 self.dict_of_dict_obj[start_dict_name][temp_key] = temp_value

The next more complicated case is to handle list of list and also user objects. I do not have any ideas on how to do it yet….