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12-Advanced Python Modules - Coggle Diagram

- - - - Defaultdict is a sub-class of the dict class that returns a dictionary-like object
      - The functionality of both dictionaries and defualtdict are almost same except for the fact that defualtdict never raises a KeyError
      - Defaultdict is a container like dictionaries present in the module collections
      - provides a default value for the key that does not exists
      - To overcome the issue when the KeyError is raised, Python introduces another dictionary like container known as Defaultdict which is present inside the collections module
      - syntax
        
        d = defaultdict(default_factory)
        
        default_factory: A function returning the default value for the dictionary defined. If this argument is absent then the dictionary raises a KeyError
      - missing()
        
        provide the default value for the dictionary
        
        takes default_factory as an argument
        
        is basically called by the getitem() method of the dict class when the requested key is not found
        
        getitem() raises or return the value returned by the missing(). method
    - - how to
        use
        
        Counter()
        with list
        
        lst = [1,2,2,2,2,3,3,3,1,2,1,12,3,2,32,1,21,1,223,1]
        Counter(lst)
        
        Counter({1: 6, 2: 6, 3: 4, 12: 1, 21: 1, 32: 1, 223: 1})
        
        Counter with strings
        
        from collections import Counter
        
        Counter with words
        in a sentence
        
        words = s.split()
        Counter(words)
        
        common pattern when
        using Counter() object
        
        dict(c)
        
        convert to a regular dictionary
        
        c.items()
        
        convert to a list of (elem, cnt) pairs
        [(a,b)]
        
        set(c)
        
        convert to a set list with all unique elements on set format
        
        Counter(dict(list_of_pairs))
        
        convert from a list of (elem, cnt) pairs
        
        list(c)
        
        lst = [1,2,2,2,2,3,3,3,1,2,1,12,3,2,32,1,21,1,223,1]
        c = Counter(lst)
        print(list(c))
        list all unique element by list format
        result: [1,2,3,12,32,223,21]
        
        list unique elements
        
        c.most_common(value)
        
        most_common(2)
        most_common()
        
        sort the dictionary and give the numbers of most common elements
        
        return the most common elements from Counter list
        
        c.clear() # reset all counts
        
        c += Counter()
        
        remove zero and negative counts
        
        sum(c.values()) # total of all counts
      - keys: element
        value: the counts of the object
      - Counter is a dict subclass which helps count hashable objects
- - - - daylight saving time: the practice with shifting their clocks one hour forward in the spring and an hour back in the fall
      - It finds its applications in situations such as the conversion of local time to UTC or to account for daylight saving time
      - some
        methods
        
        utcoffset(self, dt)
        
        time aware
        objects
        
        def utcoffset(self, dt):
        return self.stdoffset + self.dst(dt)
        
        fixed
        offset
        
        def utcoff(self, dt):
        return constant
        
        returns the difference btw time in datetime object & UTC
      - Naive and Aware
        datetime objects
        
        Aware datetime
        objects
        
        contains the time zone
        
        Naive datetime
        objects
        
        not contain any information on time zone
      - cannot be instantiated directly
  - - - do not have any information about the time zones (naive datetime object)
      - just uses the current system time
      - In some situations, the time zone details may be needed. In such cases the tzinfo abstract class is used
    - - use the datetime() class (constructor) of the datetime module
        t = datetime.datetime(2021,7,1)
      - The datetime() class also takes parameters for time and timezone (hour, minute, second, microsecond, tzone), but they are optional, and has a default value of 0, (None for timezone)
      - strftime()
        
        takes one parameter, format, to specify the format of the returned string
        
        format codes at link
        
        formatting date objects into readable strings