ch03

ch03/any.py

@@ -0,0 +1,13 @@
+items = [0, None, 0.0, True, 0, 7]  # True and 7 evaluate to True
+
+found = False  # this is called "flag"
+for item in items:
+    print('scanning item', item)
+    if item:
+        found = True  # we update the flag
+        break
+
+if found:  # we inspect the flag
+    print('At least one item evaluates to True')
+else:
+    print('All items evaluate to False')

ch03/binary.2.py

@@ -0,0 +1,8 @@
+n = 39
+remainders = []
+while n > 0:
+    n, remainder = divmod(n, 2)
+    remainders.append(remainder)
+
+remainders.reverse()
+print(remainders)

ch03/binary.py

@@ -0,0 +1,17 @@
+"""
+6 / 2 = 3 (remainder: 0)
+3 / 2 = 1 (remainder: 1)
+1 / 2 = 0 (remainder: 1)
+List of remainders: 0, 1, 1.
+Reversed is 1, 1, 0, which is also the binary repres. of 6: 110
+"""
+
+n = 39
+remainders = []
+while n > 0:
+    remainder = n % 2  # remainder of division by 2
+    remainders.append(remainder)  # we keep track of remainders
+    n //= 2  # we divide n by 2
+
+remainders.reverse()
+print(remainders)

ch03/compress.py

@@ -0,0 +1,12 @@
+from itertools import compress
+data = range(10)
+even_selector = [1, 0] * 10
+odd_selector = [0, 1] * 10
+
+even_numbers = list(compress(data, even_selector))
+odd_numbers = list(compress(data, odd_selector))
+
+print(odd_selector)
+print(list(data))
+print(even_numbers)
+print(odd_numbers)

ch03/conditional.1.py

@@ -0,0 +1,3 @@
+late = True
+if late:
+    print('I need to call my manager!')

ch03/conditional.2.py

@@ -0,0 +1,5 @@
+late = False
+if late:
+    print('I need to call my manager!')  #1
+else:
+    print('no need to call my manager...')  #2

ch03/coupons.dict.py

@@ -0,0 +1,19 @@
+customers = [
+    dict(id=1, total=200, coupon_code='F20'),  # F20: fixed, £20
+    dict(id=2, total=150, coupon_code='P30'),  # P30: percent, 30%
+    dict(id=3, total=100, coupon_code='P50'),  # P50: percent, 50%
+    dict(id=4, total=110, coupon_code='F15'),  # F15: fixed, £15
+]
+discounts = {
+    'F20': (0.0, 20.0),  # each value is (percent, fixed)
+    'P30': (0.3, 0.0),
+    'P50': (0.5, 0.0),
+    'F15': (0.0, 15.0),
+}
+for customer in customers:
+    code = customer['coupon_code']
+    percent, fixed = discounts.get(code, (0.0, 0.0))
+    customer['discount'] = percent * customer['total'] + fixed
+
+for customer in customers:
+    print(customer['id'], customer['total'], customer['discount'])

ch03/coupons.py

@@ -0,0 +1,21 @@
+customers = [
+    dict(id=1, total=200, coupon_code='F20'),  # F20: fixed, £20
+    dict(id=2, total=150, coupon_code='P30'),  # P30: percent, 30%
+    dict(id=3, total=100, coupon_code='P50'),  # P50: percent, 50%
+    dict(id=4, total=110, coupon_code='F15'),  # F15: fixed, £15
+]
+for customer in customers:
+    code = customer['coupon_code']
+    if code == 'F20':
+        customer['discount'] = 20.0
+    elif code == 'F15':
+        customer['discount'] = 15.0
+    elif code == 'P30':
+        customer['discount'] = customer['total'] * 0.3
+    elif code == 'P50':
+        customer['discount'] = customer['total'] * 0.5
+    else:
+        customer['discount'] = 0.0
+
+for customer in customers:
+    print(customer['id'], customer['total'], customer['discount'])

ch03/discount.py

@@ -0,0 +1,17 @@
+from datetime import date, timedelta
+
+today = date.today()
+tomorrow = today + timedelta(days=1)  # today + 1 day is tomorrow
+products = [
+    {'sku': '1', 'expiration_date': today, 'price': 100.0},
+    {'sku': '2', 'expiration_date': tomorrow, 'price': 50},
+    {'sku': '3', 'expiration_date': today, 'price': 20},
+]
+
+for product in products:
+    if product['expiration_date'] != today:
+        continue
+    product['price'] *= 0.8  # equivalent to applying 20% discount
+    print(
+        'Price for sku', product['sku'],
+        'is now', product['price'])

ch03/errorsalert.py

@@ -0,0 +1,18 @@
+# The send_email function is defined here to enable you to play with
+# code, but of course it doesn't send an actual email.
+def send_email(*a):
+    print (*a)
+
+alert_system = 'console'  # other value can be 'email'
+error_severity = 'critical'  # other values: 'medium' or 'low'
+error_message = 'OMG! Something terrible happened!'
+
+if alert_system == 'console':
+    print(error_message)  #1
+elif alert_system == 'email':
+    if error_severity == 'critical':
+        send_email('admin@example.com', error_message)  #2
+    elif error_severity == 'medium':
+        send_email('support.1@example.com', error_message)  #3
+    else:
+        send_email('support.2@example.com', error_message)  #4

ch03/for.else.py

@@ -0,0 +1,11 @@
+class DriverException(Exception):
+    pass
+
+
+people = [('James', 17), ('Kirk', 9), ('Lars', 13), ('Robert', 8)]
+for person, age in people:
+    if age >= 18:
+        driver = (person, age)
+        break
+else:
+    raise DriverException('Driver not found.')

ch03/for.no.else.py

@@ -0,0 +1,13 @@
+class DriverException(Exception):
+    pass
+
+
+people = [('James', 17), ('Kirk', 9), ('Lars', 13), ('Robert', 8)]
+driver = None
+for person, age in people:
+    if age >= 18:
+        driver = (person, age)
+        break
+
+if driver is None:
+    raise DriverException('Driver not found.')

ch03/infinite.py

@@ -0,0 +1,8 @@
+from itertools import count
+
+for n in count(5, 3):
+    if n > 20:
+        break
+    print(n, end=', ')  # instead of newline, comma and space
+
+print()

ch03/menu.no.walrus.py

@@ -0,0 +1,13 @@
+flavors = ["pistachio", "malaga", "vanilla", "chocolate", "strawberry"]
+prompt = "Choose your flavor: "
+
+print(flavors)
+
+while True:
+    choice = input(prompt)
+    if choice in flavors:
+        break
+
+    print(f"Sorry, '{choice}' is not a valid option.")
+
+print(f"You chose '{choice}'.")

ch03/menu.walrus.py

@@ -0,0 +1,9 @@
+flavors = ["pistachio", "malaga", "vanilla", "chocolate", "strawberry"]
+prompt = "Choose your flavor: "
+
+print(flavors)
+
+while (choice := input(prompt)) not in flavors:
+    print(f"Sorry, '{choice}' is not a valid option.")
+
+print(f"You chose '{choice}'.")

ch03/multiple.sequences.enumerate.py

@@ -0,0 +1,5 @@
+people = ['Nick', 'Rick', 'Roger', 'Syd']
+ages = [23, 24, 23, 21]
+for position, person in enumerate(people):
+    age = ages[position]
+    print(person, age)

ch03/multiple.sequences.explicit.py

@@ -0,0 +1,5 @@
+people = ['Nick', 'Rick', 'Roger', 'Syd']
+ages = [23, 24, 23, 21]
+instruments = ['Drums', 'Keyboards', 'Bass', 'Guitar']
+for person, age, instrument in zip(people, ages, instruments):
+    print(person, age, instrument)

ch03/multiple.sequences.implicit.py

@@ -0,0 +1,6 @@
+people = ['Nick', 'Rick', 'Roger', 'Syd']
+ages = [23, 24, 23, 21]
+instruments = ['Drums', 'Keyboards', 'Bass', 'Guitar']
+for data in zip(people, ages, instruments):
+    person, age, instrument = data
+    print(person, age, instrument)

ch03/multiple.sequences.py

@@ -0,0 +1,6 @@
+people = ['Nick', 'Rick', 'Roger', 'Syd']
+ages = [23, 24, 23, 21]
+for position in range(len(people)):
+    person = people[position]
+    age = ages[position]
+    print(person, age)

ch03/multiple.sequences.while.py

@@ -0,0 +1,8 @@
+people = ['Nick', 'Rick', 'Roger', 'Syd']
+ages = [23, 24, 23, 21]
+position = 0
+while position < len(people):
+    person = people[position]
+    age = ages[position]
+    print(person, age)
+    position += 1

ch03/multiple.sequences.zip.py

@@ -0,0 +1,4 @@
+people = ['Nick', 'Rick', 'Roger', 'Syd']
+ages = [23, 24, 23, 21]
+for person, age in zip(people, ages):
+    print(person, age)

ch03/permutations.py

@@ -0,0 +1,2 @@
+from itertools import permutations
+print(list(permutations('ABC')))

ch03/primes.else.py

@@ -0,0 +1,10 @@
+primes = []
+upto = 100
+for n in range(2, upto + 1):
+    for divisor in range(2, n):
+        if n % divisor == 0:
+            break
+    else:
+        primes.append(n)
+
+print(primes)

ch03/primes.py

@@ -0,0 +1,12 @@
+primes = []  # this will contain the primes in the end
+upto = 100  # the limit, inclusive
+for n in range(2, upto + 1):
+    is_prime = True  # flag, new at each iteration of outer for
+    for divisor in range(2, n):
+        if n % divisor == 0:
+            is_prime = False
+            break
+    if is_prime:  # check on flag
+        primes.append(n)
+
+print(primes)

ch03/range.py

@@ -0,0 +1,6 @@
+>>> list(range(10))  # one value: from 0 to value (excluded)
+[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+>>> list(range(3, 8))  # two values: from start to stop (excluded)
+[3, 4, 5, 6, 7]
+>>> list(range(-10, 10, 4))  # three values: step is added
+[-10, -6, -2, 2, 6]

ch03/simple.for.2.py

@@ -0,0 +1,4 @@
+surnames = ['Rivest', 'Shamir', 'Adleman']
+for position in range(len(surnames)):
+    print(position, surnames[position])
+    # print(surnames[position][0], end='')  # try swapping prints

ch03/simple.for.3.py

@@ -0,0 +1,3 @@
+surnames = ['Rivest', 'Shamir', 'Adleman']
+for surname in surnames:
+    print(surname)

ch03/simple.for.4.py

@@ -0,0 +1,3 @@
+surnames = ['Rivest', 'Shamir', 'Adleman']
+for position, surname in enumerate(surnames):
+    print(position, surname)

ch03/simple.for.py

@@ -0,0 +1,7 @@
+for number in [0, 1, 2, 3, 4]:
+    print(number)
+
+
+# equivalent using range
+for number in range(5):
+    print(number)

ch03/switch.js

@@ -0,0 +1,18 @@
+switch (day_number) {
+    case 1:
+    case 2:
+    case 3:
+    case 4:
+    case 5:
+        day = "Weekday";
+        break;
+    case 6:
+        day = "Saturday";
+        break;
+    case 0:
+        day = "Sunday";
+        break;
+    default:
+        day = "";
+        alert(day_number + ' is not a valid day number.')
+}

ch03/switch.py

@@ -0,0 +1,11 @@
+# this code is not supposed to be run
+if 1 <= day_number <= 5:
+    day = 'Weekday'
+elif day_number == 6:
+    day = 'Saturday'
+elif day_number == 0:
+    day = 'Sunday'
+else:
+    day = ''
+    raise ValueError(
+        str(day_number) + ' is not a valid day number.')

ch03/taxes.py

@@ -0,0 +1,11 @@
+income = 15000
+if income < 10000:
+    tax_coefficient = 0.0  #1
+elif income < 30000:
+    tax_coefficient = 0.2  #2
+elif income < 100000:
+    tax_coefficient = 0.35  #3
+else:
+    tax_coefficient = 0.45  #4
+
+print(f'You will pay: ${income * tax_coefficient} in taxes')

ch03/ternary.py

@@ -0,0 +1,12 @@
+order_total = 247  # GBP
+
+# classic if/else form
+if order_total > 100:
+    discount = 25  # GBP
+else:
+    discount = 0  # GBP
+print(order_total, discount)
+
+# ternary operator
+discount = 25 if order_total > 100 else 0
+print(order_total, discount)

ch03/walrus.if.py

@@ -0,0 +1,12 @@
+value = 42
+modulus = 11
+
+# Without assignment expression:
+remainder = value % modulus
+if remainder:
+    print(f"Not divisible! The remainder is {remainder}.")
+
+
+# Rewritten with assignment expression:
+if remainder := value % modulus:
+    print(f"Not divisible! The remainder is {remainder}.")