ch02

Author: adii1823

ch02/README.md

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+Chapter 2 data files
+====================
+
+The files in this folder are not supposed to work if run.
+They serve as source for the book chapters, and to provide a
+quick copy/paste tool for whoever would need their content.

ch02/bytearray.py

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+# bytearray.py
+
+
+>>> bytearray()  # empty bytearray object
+bytearray(b'')
+>>> bytearray(10)  # zero-filled instance with given length
+bytearray(b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')
+>>> bytearray(range(5))  # bytearray from iterable of integers
+bytearray(b'\x00\x01\x02\x03\x04')
+>>> name = bytearray(b'Lina')  #A - bytearray from bytes
+>>> name.replace(b'L', b'l')
+bytearray(b'lina')
+>>> name.endswith(b'na')
+True
+>>> name.upper()
+bytearray(b'LINA')
+>>> name.count(b'L')
+1

ch02/chainmap.py

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+# chainmap.py
+
+
+>>> from collections import ChainMap
+>>> default_connection = {'host': 'localhost', 'port': 4567}
+>>> connection = {'port': 5678}
+>>> conn = ChainMap(connection, default_connection) # map creation
+>>> conn['port']  # port is found in the first dictionary
+5678
+>>> conn['host']  # host is fetched from the second dictionary
+'localhost'
+>>> conn.maps  # we can see the mapping objects
+[{'port': 5678}, {'host': 'localhost', 'port': 4567}]
+>>> conn['host'] = 'packtpub.com'  # let's add host
+>>> conn.maps
+[{'port': 5678, 'host': 'packtpub.com'},
+ {'host': 'localhost', 'port': 4567}]
+>>> del conn['port']  # let's remove the port information
+>>> conn.maps
+[{'host': 'packtpub.com'}, {'host': 'localhost', 'port': 4567}]
+>>> conn['port']  # now port is fetched from the second dictionary
+4567
+>>> dict(conn)  # easy to merge and convert to regular dictionary
+{'host': 'packtpub.com', 'port': 4567}

ch02/dateandtime.py

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+
+# imports
+>>> from datetime import date, datetime, timedelta, timezone
+>>> import time
+>>> import calendar as cal
+>>> from zoneinfo import ZoneInfo
+
+
+# date
+>>> today = date.today()
+>>> today
+datetime.date(2021, 3, 28)
+>>> today.ctime()
+'Sun Mar 28 00:00:00 2021'
+>>> today.isoformat()
+'2021-03-28'
+>>> today.weekday()
+6
+>>> cal.day_name[today.weekday()]
+'Sunday'
+>>> today.day, today.month, today.year
+(28, 3, 2021)
+>>> today.timetuple()
+time.struct_time(
+    tm_year=2021, tm_mon=3, tm_mday=28,
+    tm_hour=0, tm_min=0, tm_sec=0,
+    tm_wday=6, tm_yday=87, tm_isdst=-1
+)
+
+# time
+>>> time.ctime()
+'Sun Mar 28 15:23:17 2021'
+>>> time.daylight
+1
+>>> time.gmtime()
+time.struct_time(
+    tm_year=2021, tm_mon=3, tm_mday=28,
+    tm_hour=14, tm_min=23, tm_sec=34,
+    tm_wday=6, tm_yday=87, tm_isdst=0
+)
+>>> time.gmtime(0)
+time.struct_time(
+    tm_year=1970, tm_mon=1, tm_mday=1,
+    tm_hour=0, tm_min=0, tm_sec=0,
+    tm_wday=3, tm_yday=1, tm_isdst=0
+)
+>>> time.localtime()
+time.struct_time(
+    tm_year=2021, tm_mon=3, tm_mday=28,
+    tm_hour=15, tm_min=23, tm_sec=50,
+    tm_wday=6, tm_yday=87, tm_isdst=1
+)
+>>> time.time()
+1616941458.149149
+
+
+# datetime, timezones and tiemdeltas
+>>> now = datetime.now()
+>>> utcnow = datetime.utcnow()
+>>> now
+datetime.datetime(2021, 3, 28, 15, 25, 16, 258274)
+>>> utcnow
+datetime.datetime(2021, 3, 28, 14, 25, 22, 918195)
+>>> now.date()
+datetime.date(2021, 3, 28)
+>>> now.day, now.month, now.year
+(28, 3, 2021)
+>>> now.date() == date.today()
+True
+>>> now.time()
+datetime.time(15, 25, 16, 258274)
+>>> now.hour, now.minute, now.second, now.microsecond
+(15, 25, 16, 258274)
+>>> now.ctime()
+'Sun Mar 28 15:25:16 2021'
+>>> now.isoformat()
+'2021-03-28T15:25:16.258274'
+>>> now.timetuple()
+time.struct_time(
+    tm_year=2021, tm_mon=3, tm_mday=28,
+    tm_hour=15, tm_min=25, tm_sec=16,
+    tm_wday=6, tm_yday=87, tm_isdst=-1
+)
+>>> now.tzinfo
+>>> utcnow.tzinfo
+>>> now.weekday()
+6
+>>> f_bday = datetime(
+    1975, 12, 29, 12, 50, tzinfo=ZoneInfo('Europe/Rome')
+)
+>>> h_bday = datetime(
+    1981, 10, 7, 15, 30, 50, tzinfo=timezone(timedelta(hours=2))
+)
+>>> diff = h_bday - f_bday
+>>> type(diff)
+<class 'datetime.timedelta'>
+>>> diff.days
+2109
+>>> diff.total_seconds()
+182223650.0
+>>> today + timedelta(days=49)
+datetime.date(2021, 5, 16)
+>>> now + timedelta(weeks=7)
+datetime.datetime(2021, 5, 16, 15, 25, 16, 258274)
+
+
+# parsing (stdlib)
+>>> datetime.fromisoformat('1977-11-24T19:30:13+01:00')
+datetime.datetime(
+    1977, 11, 24, 19, 30, 13,
+    tzinfo=datetime.timezone(datetime.timedelta(seconds=3600))
+)
+
+>>> datetime.fromtimestamp(time.time())
+datetime.datetime(2021, 3, 28, 15, 42, 2, 142696)
+
+>>> datetime.now()
+datetime.datetime(2021, 3, 28, 15, 42, 1, 120094)
+
+
+# arrow small demo
+>>> import arrow
+>>> arrow.utcnow()
+<Arrow [2021-03-28T14:43:20.017213+00:00]>
+>>> arrow.now()
+<Arrow [2021-03-28T15:43:39.370099+01:00]>
+
+>>> local = arrow.now('Europe/Rome')
+>>> local
+<Arrow [2021-03-28T16:59:14.093960+02:00]>
+>>> local.to('utc')
+<Arrow [2021-03-28T14:59:14.093960+00:00]>
+>>> local.to('Europe/Moscow')
+<Arrow [2021-03-28T17:59:14.093960+03:00]>
+>>> local.to('Asia/Tokyo')
+<Arrow [2021-03-28T23:59:14.093960+09:00]>
+>>> local.datetime
+datetime.datetime(
+    2021, 3, 28, 16, 59, 14, 93960,
+    tzinfo=tzfile('/usr/share/zoneinfo/Europe/Rome')
+)
+>>> local.isoformat()
+'2021-03-28T16:59:14.093960+02:00'

ch02/defaultdict.py

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+# defaultdict.py
+
+
+>>> d = {}
+>>> d['age'] = d.get('age', 0) + 1  # age not there, we get 0 + 1
+>>> d
+{'age': 1}
+>>> d = {'age': 39}
+>>> d['age'] = d.get('age', 0) + 1  # age is there, we get 40
+>>> d
+{'age': 40}
+
+
+>>> from collections import defaultdict
+>>> dd = defaultdict(int)  # int is the default type (0 the value)
+>>> dd['age'] += 1  # short for dd['age'] = dd['age'] + 1
+>>> dd
+defaultdict(<class 'int'>, {'age': 1})  # 1, as expected

ch02/dicts.py

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+# dicts.py
+
+
+>>> a = dict(A=1, Z=-1)
+>>> b = {'A': 1, 'Z': -1}
+>>> c = dict(zip(['A', 'Z'], [1, -1]))
+>>> d = dict([('A', 1), ('Z', -1)])
+>>> e = dict({'Z': -1, 'A': 1})
+>>> a == b == c == d == e  # are they all the same?
+True  # They are indeed
+
+
+# zip
+>>> list(zip(['h', 'e', 'l', 'l', 'o'], [1, 2, 3, 4, 5]))
+[('h', 1), ('e', 2), ('l', 3), ('l', 4), ('o', 5)]
+>>> list(zip('hello', range(1, 6)))  # equivalent, more pythonic
+[('h', 1), ('e', 2), ('l', 3), ('l', 4), ('o', 5)]
+
+
+# basic
+>>> d = {}
+>>> d['a'] = 1  # let's set a couple of (key, value) pairs
+>>> d['b'] = 2
+>>> len(d)  # how many pairs?
+2
+>>> d['a']  # what is the value of 'a'?
+1
+>>> d  # how does `d` look now?
+{'a': 1, 'b': 2}
+>>> del d['a']  # let's remove `a`
+>>> d
+{'b': 2}
+>>> d['c'] = 3  # let's add 'c': 3
+>>> 'c' in d  # membership is checked against the keys
+True
+>>> 3 in d  # not the values
+False
+>>> 'e' in d
+False
+>>> d.clear()  # let's clean everything from this dictionary
+>>> d
+{}
+
+
+
+# views
+>>> d = dict(zip('hello', range(5)))
+>>> d
+{'h': 0, 'e': 1, 'l': 3, 'o': 4}
+>>> d.keys()
+dict_keys(['h', 'e', 'l', 'o'])
+>>> d.values()
+dict_values([0, 1, 3, 4])
+>>> d.items()
+dict_items([('h', 0), ('e', 1), ('l', 3), ('o', 4)])
+>>> 3 in d.values()
+True
+>>> ('o', 4) in d.items()
+True
+
+
+# other methods
+>>> d
+{'h': 0, 'e': 1, 'l': 3, 'o': 4}
+>>> d.popitem()  # removes a random item (useful in algorithms)
+('o', 4)
+>>> d
+{'h': 0, 'e': 1, 'l': 3}
+>>> d.pop('l')  # remove item with key `l`
+3
+>>> d.pop('not-a-key')  # remove a key not in dictionary: KeyError
+Traceback (most recent call last):
+  File "<stdin>", line 1, in <module>
+KeyError: 'not-a-key'
+>>> d.pop('not-a-key', 'default-value')  # with a default value?
+'default-value'  # we get the default value
+>>> d.update({'another': 'value'})  # we can update dict this way
+>>> d.update(a=13)  # or this way (like a function call)
+>>> d
+{'h': 0, 'e': 1, 'another': 'value', 'a': 13}
+>>> d.get('a')  # same as d['a'] but if key is missing no KeyError
+13
+>>> d.get('a', 177)  # default value used if key is missing
+13
+>>> d.get('b', 177)  # like in this case
+177
+>>> d.get('b')  # key is not there, so None is returned
+
+
+# setdefault
+>>> d = {}
+>>> d.setdefault('a', 1)  # 'a' is missing, we get default value
+1
+>>> d
+{'a': 1}  # also, the key/value pair ('a', 1) has now been added
+>>> d.setdefault('a', 5)  # let's try to override the value
+1
+>>> d
+{'a': 1}  # no override, as expected
+
+
+# setdefault example
+>>> d = {}
+>>> d.setdefault('a', {}).setdefault('b', []).append(1)
+>>> d
+{'a': {'b': [1]}}
+
+
+# union
+>>> d = {'a': 'A', 'b': 'B'}
+>>> e = {'b': 8, 'c': 'C'}
+>>> d | e
+{'a': 'A', 'b': 8, 'c': 'C'}
+>>> e | d
+{'b': 'B', 'c': 'C', 'a': 'A'}
+>>> {**d, **e}
+{'a': 'A', 'b': 8, 'c': 'C'}
+>>> {**e, **d}
+{'b': 'B', 'c': 'C', 'a': 'A'}
+
+>>> d |= e
+>>> d
+{'a': 'A', 'b': 8, 'c': 'C'}

ch02/enum.py

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+>>> GREEN = 1
+>>> YELLOW = 2
+>>> RED = 4
+>>> TRAFFIC_LIGHTS = (GREEN, YELLOW, RED)
+>>> # or with a dict
+>>> traffic_lights = {'GREEN': 1, 'YELLOW': 2, 'RED': 4}
+
+
+
+# using enum
+>>> from enum import Enum
+>>> class TrafficLight(Enum):
+...     GREEN = 1
+...     YELLOW = 2
+...     RED = 4
+...
+>>> TrafficLight.GREEN
+<TrafficLight.GREEN: 1>
+>>> TrafficLight.GREEN.name
+'GREEN'
+>>> TrafficLight.GREEN.value
+1
+>>> TrafficLight(1)
+<TrafficLight.GREEN: 1>
+>>> TrafficLight(4)
+<TrafficLight.RED: 4>