Thanks Peter , Terry and others ! On Tue, Apr 4, 2017 at 12:11 PM, Peter Otten <__pete...@web.de> wrote:
> Ganesh Pal wrote: > > >> > >> > >> Whenever you feel the urge to write range(len(whatever)) -- resist that > >> temptation, and you'll end up with better Python code ;) > >> > >> > > Thanks for this suggestion but for my better understanding can explain > > this further even Steve did point the same mistake. > > It's not directly a mistake, it's just that programming against a smaller > interface makes your code more flexible and more readable. > > Readability: > > items = [...] > for i in range(len(items)): > ... > > Are list entries replaced? We cannot know without inspecting the for suite. > > items = [...] > for item in items: > ... > > Are list entries replaced? No. > > Flexibility: > > def give_raise(employees, amount): > for i in range(len(items)): > employee = employees[i] > employee.payment += amount > > employees = [...] > give_raise(employees, 10) > > Now let's adapt the code to raise the payment of some employees: > > male_employees = [ > employees[i] for i in range(len(employees)) > if e.sex == "male" > ] > give_raise(male_emplyees, 10) > > We need a helper list, basically because there is a len() call inside the > give_raise() function. If we rewrite the function in an idiomatic way > > def give_raise(employees, amount): > for employee in employees: > employee.payment += amount > > it will become not just more concise, the calling code no longer needs to > build the intermediate list. Instead we save the extra memory and pass a > generator expression: > > give_raise((e for e in employees if e.sex == "female"), 10) > > In a similar way you can write code that iterates over data that is lazily > read into memory, like lines in a file > > # wrong, reads the whole file into memory > lines = open(...).readlines() > for i in range(len(lines)): > process(lines[i]) > > # idiomatic, read the lines as needed > for line in open(...): > process(line) > > or records from a database. > > > > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
