On 2/28/17, 3:32 AM, "Tutor on behalf of Peter Otten" <tutor-bounces+ryan=allwegot....@python.org on behalf of __pete...@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" > > >_______________________________________________ >Tutor maillist - Tutor@python.org >To unsubscribe or change subscription options: >https://mail.python.org/mailman/listinfo/tutor > 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 _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
