[Tutor] feedback on simple python code

[Ryan Smith]

On 2/28/17, 3:32 AM, "Tutor on behalf of Peter Otten"
<tutor-bounces+ryan=allwegot.net at python.org on behalf of __peter__ at web.de>
wrote:

>Ryan Smith wrote:
>
>> Hi all,
>> 
>> New python student here. I have been using O¹reilly¹s "Python Beyond the
>> Basics: Object Oriented Programming video series". In one of the
>> assignments we are to write a simple inheritance hierarchy of three
>> classes that write to text files. I have actually written the code for
>>the
>> assignment and it runs as well as meets the requirements of the
>> assignment. I am posting to get feedback on how I can improve this and
>> making it more pythonic and concise.
>> 
>> Please keep in mind that I am simply ³simulating" writing to a log file
>> and a tabbed delimited file, so I¹m not necessarily looking for which
>> modules I could have to create actual log files or writing to actual csv
>> files. The output of the code should be two text files with text written
>> to them that have been passed to the instance of each respective object.
>> 
>> #!/usr/bin/env python
>> 
>> import abc
>> import datetime
>> 
>> class WriteFile(object):
>>     __metaclass__ = abc.ABCMeta
>>     
>>     
>>     @abc.abstractmethod
>>     def write(self,text):
>
>You might run a tool like https://pypi.python.org/pypi/pycodestyle over
>your 
>code to ensure it follows common standards.
>
>>         """Write to file"""
>>         return
>>     
>> 
>> class LogFile(WriteFile):
>>     def __init__(self,fh):
>>     self.fh = fh
>>         
>> 
>>     def write(self, text):
>>     date = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
>>     entry = "{0} {1}{2}".format(date, text, '\n')
>>     with open(self.fh, 'a') as f:
>>     f.write(entry)
>> 
>> class DelimWrite(WriteFile):
>>     def __init__(self, fh, delim):
>>     self.fh = fh
>>     self.delim = delim
>>         
>> 
>>     def write(self, text):
>>     with open(self.fh, 'a') as f:
>>         entry = ""
>>         for item in text:
>>             if self.delim in item:
>> entry += ' "{0}"{1} '.format(item,self.delim)
>
>What will happen if text contains double quotes?
>
>> else:
>>                 entry += item+self.delim
>
>Have a look at the str.join() method. Example:
>
>>>> ",".join(["foo", "bar", "baz"])
>'foo,bar,baz'
>
>>         f.write(entry.strip(self.delim) + '\n')
>
>I will mention another "principle", DRY (don't repeat yourself), i. e. do
>not write the same code twice.
>
>When I look at your code I see that both DelimWrite and LogFile open a
>file. 
>If you want modify your code to accept file objects like sys.stdout you
>have 
>to make changes in both subclasses. To avoid that you might put the file-
>writing part into a separate method:
>
>class WriteFile(object):
>    def __init__(self, file):
>        self.file = file
>
>    def write_record(self, record):
>        with open(self.file, "a") as f:
>            f.write(self.format_record(record))
>
>    def format_record(self, record):
>        return record
>
>
>class LogFile(WriteFile):
>    def format_record(self, record):
>        date = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')
>        return "{0} {1}\n".format(date, record)
>
>
>class DelimWrite(WriteFile):
>    quote = '"'
>    def __init__(self, file, delimiter):
>        super(DelimWrite, self).__init__(file)
>        self.delimiter = delimiter
>
>    def escaped(self, value):
>        value = str(value)
>        if self.delimiter in value:
>            quote = self.quote
>            value = '"{}"'.format(value.replace(quote, quote + quote))
>        return value
>
>    def format_record(self, record):
>        escaped_rows = (self.escaped(value) for value in record)
>        return self.delimiter.join(escaped_rows) + "\n"
>
>
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Danny/Peter,

Thank you to both of you for your feedback.

Peter,

I will definitely be adding pycodestyle to my toolkit. You made a good
point about creating a separate method for file writing so that both the
DelimWrite and the LogFile classes can use them. Also looking at my code I
see where my code does repeat with the write() method. I guess I’m still
trying to understand polymorphism because that’s what I was aiming for
when I wrote the code.

Danny,

Thank you for the link you provided on Liskov’s principals. To be honest I
started reading what you shared and realize it’s gonna take a little time
to digest it so that I can apply the principals in future code. I’m sure I
will have more questions, but I will just start a separate thread.

Again thank you both,

Ryan