Python_Comprehend_Daily

2017-12-21
  • argparse
    • add_argument
      • const/default: these two attribute can not only be const like 1 or one, but can be function like max/sum/all
  • curses
    • getch(): window.getch()/stdscr.getch()

  • list/tuple

    • tuple: 
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      tuple1 = ([1, 2, 3],(4, 5, 6), (7, 8, 9))
      tuple2 = ((1, 2, 3),(4, 5, 6), (7, 8, 9))
      type(tuple1[0]) = list
      type(tuple1[1]) = tuple
      type(list(tuple1[1])) = list

  • defaultdict

    • source: collections

    • notes

      • TypeError: first argument must be callable or None

        • For a defaultdict, the default value is usually not really a value, it is a factory: a method that generates a new value.

        • Example:

          • Wrong:

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            lst = list(range(0, 5))
            d = defaultdict(lst)

            the terminal will report an error like this:

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            TypeError: first argument must be callable or None

          • Right:

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            d = defaultdict(lambda: list(range(0, 5)))

        • Extend: the codes below will make all default values(like d[1]/d[2]) reference the same list

          • Example:

            • Wrong:

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              >>> val = list(range(0, 5))
              >>> d = defaultdict(lambda: val)
              >>> d[1]
              [0, 1, 2, 3, 4]
              >>> d[1].append(14)
              >>> d[2]
              [0, 1, 2, 3, 4, 14]

            • Right:

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              >>> val = lambda: list(range(0, 5))
              >>> d = defaultdict(val)
              >>> d[1]
              [0, 1, 2, 3, 4]
              >>> d[1].append(14)
              >>> d[2]
              [0, 1, 2, 3, 4]

          • Reason: