CODEWITHSUNDEEP
pythonfunctionsorting
S. Orlowski
S. Orlowski

Reputation: 35

Python sort dates

im newbie in Python and i got task to sort dates in dictionary by year, month, day.

I found one nice method from W3Schools but i dont know how to work one thing. Below is code

def myFunc(e):
  return e['year']

cars = [
  {'car': 'Ford', 'year': 2005},
  {'car': 'Mitsubishi', 'year': 2000},
  {'car': 'BMW', 'year': 2019},
  {'car': 'VW', 'year': 2011}
]

cars.sort(key=myFunc)

print(cars)

Its working good to sort for example cars by year, also to dates by year, month, day but i have question. How this method is working and why there is 'e' which i didnt use in cars.sort(key=myFunc)? Why this 'key=myFunc' myFunc is without argument? Can i write it without this function? My main language is Java so its abstract for me and maybe someone can explain this.

def myFunc(e):
  return e['year']

I have read doc about sort but still i dont understand this function.

Upvotes: 1

Views: 94

Answers (1)

Zingerella
Zingerella

Reputation: 450

In python you can pass functions as arguments. sort can take a function as its sorting key. I suggest looking up tutorials on python syntax, functions, python dict, and sorting lists.

To answer your question briefly, cars is a list that has multiple dictionary elements. cars.sort() needs to know how to sort these elements (there is no clear way to sort something abstract like that).

That's where key=myFunc comes in handy. cars.sort() will give myFunc an element, then myFunc receives that element as whatever parameter you have in its header. Here, you have e as the dictionary element since def myFunc(e) is your header. The function returns the year of the dictionary element by getting e['year']. This year is returned to the cars.sort() which now knows that it must sort the dictionary elements by this year value that was returned.

Upvotes: 2

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