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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 Using Python as a Calculator
Let's try some simple python commands
Numbers
The interpreter acts as a simple calculator
Step1:  With Python, use ** operator to calculate powers.
Step2:  Use equal sign(=) to assign a value to variable like math variable.
Step3:  If a variable is not defined (assigned a value), trying to use it will give you an error
Step4:  List
Python knows a number of compound data types, used to group together other values. The most versatile is the list, which can be written as a list of comma-separated values (items) between square brackets. Lists might contain items of different types, but usually the items all have the same type.
Step5:  List can be indexed, with the first item having index 0.
Step6:  In addition to indexing, slicing is also supported. While indexing is used to obtain individual item, slicing allows you to obtain sub-list
Step7:  You can replace the item in the list and add new items at the end of the list.
Step8:  List support the + operation.
Step9:  Strings
Besides numbers, Python can also manipulate strings, which can be expressed in several ways. They can be enclosed in single quotes ('...') or double quotes ("...") with the same result. \ can be used to escape quotes
Step10:  String also support indexing and slicing like list. You can see the string as a list of charaters.
Step11:  Python Iteration
Step12:  Bool Type
Like most languages, Python also has bool Type
Step13:  Use bool operators to create bool type
Step14:  Other functions may also create bool type.
Step15:  Dict
Dict is another very important data structure in python
Comparing to list, it is a unordered sets or objects
Moreover, the item are accessed via keys and not via their position
Step16:  Conditional Statement
Conditional statement are used to execute code fragments based on a condition.
The most commonly used construct is if-else and while statement
Step17:  Function
Step18:  Exercises 1
Please construct a function named productEven which imput a list of integers and return the product of the even numbers in the list.
For example
Step19:  Exercises 2
Write a code which will find all such numbers which are divisible by 7 but are not a multiple of 5,
between 2000 and 3200 (both included).
Step20:  Exercises 3
Write a python program to count the number 4 in a given list.
Step21:  Exercises 4
Write a Python program to compute the greatest common divisor (GCD) of two positive integers.
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Python Code:
4
2 + 2
50 - 5*6
(50-5)*6
8/5
8//5  # Floor division discards the fractional part
8%5  # The % operator return the remainder of the division
Explanation: Using Python as a Calculator
Let's try some simple python commands
Numbers
The interpreter acts as a simple calculator: you can type an expression at it and it will write the value. Expression syntax is straightforward: the operators +, -, * and / work just like in most other languages (for example, Pascal or C); parentheses (()) can be used for grouping.
End of explanation
5 ** 3  # 5 squared
type(4)
type(1.3)
Explanation: With Python, use ** operator to calculate powers.
End of explanation
width = 30
width
width = 30
height = 2
width * height
Explanation: Use equal sign(=) to assign a value to variable like math variable.
End of explanation
s = 3 * 4
s   # Try to access an undefined variable
print(5)
print(width)
Explanation: If a variable is not defined (assigned a value), trying to use it will give you an error:
End of explanation
empty_list = []
empty_list
type(empty_list)
squares = [1, 4, 9, 16, 25]
squares
Explanation: List
Python knows a number of compound data types, used to group together other values. The most versatile is the list, which can be written as a list of comma-separated values (items) between square brackets. Lists might contain items of different types, but usually the items all have the same type.
End of explanation
squares[0]
squares[1]
len(squares)
squares[len(squares) - 1]
squares[-1]  # Last item
squares[-2]  # Second-last item
Explanation: List can be indexed, with the first item having index 0.
End of explanation
squares = [1, 2, 3, 4, 5]
squares[1:4]  # Get sub-list from the 1 to 4 with step size 1
squares[1:4:2]  # Get sub-list from 1 to 4 with step size 2
squares[:4]  # from begining of the list to 4 with step size 1
squares[1:]  # from 1 to the end of the list with step size 1
squares[::2]  # from begining to the end with step size 2
Explanation: In addition to indexing, slicing is also supported. While indexing is used to obtain individual item, slicing allows you to obtain sub-list:
Format of slicing: begin:end:step_size
End of explanation
names = []
names.append('John')
names
names.append('Paul')
names
names[1] = 'Alice'
names
names2 = ['Ryan', 'Tang']
names2
names = names + names2
names
names.append(['Fang', 'HE'])
names
squares.append(11)
squares
squares[1:3] = [12, 13, 14] 
squares
len(squares)  # calculate the number of item in the list
Explanation: You can replace the item in the list and add new items at the end of the list.
End of explanation
list1 = [1, 2]
list2 = [3, 4]
list3 = list1 + list2
list3
list1 = [1, 2, 3]
list2 = [x**2 for x in list1]
list2
Explanation: List support the + operation.
End of explanation
'Hello World!'
type('hello')
'doesn\'t'
s = 'Hello World'
s
Explanation: Strings
Besides numbers, Python can also manipulate strings, which can be expressed in several ways. They can be enclosed in single quotes ('...') or double quotes ("...") with the same result. \ can be used to escape quotes:
End of explanation
s[1:]
s[-1]
s1 = 'Hello '
s2 = 'World!'
s3 = s1 + s2
s3
s3.isdigit()
s3.isupper()
s3.lower()
Explanation: String also support indexing and slicing like list. You can see the string as a list of charaters.
End of explanation
squares = [1, 4, 9, 16, 25]
for s in squares:
    print(s)
for i in range(10):
    print(i)
for i in range(1, 10):
    print(i)
for i in range(1, 10, 2):
    print(i)
N = 8
fact = 1
for i in range(1, N+1):
    fact = fact * i
fact
# For any i, we list the integer less than i
for i in range(5):
    print("i=", i)
    l = []
    for j in range(0,i):
        l.append(j)
    print(l)
        
Explanation: Python Iteration
End of explanation
True
False
type(True)
Explanation: Bool Type
Like most languages, Python also has bool Type: True and False.
End of explanation
3 > 1
3 < 1
3 == 1
3 == 3
3 != 2
b = 3 > 4
b
Explanation: Use bool operators to create bool type
End of explanation
even_number = [2, 4, 6, 8, 10, 12]
even_number
6 in even_number
3 in even_number
Explanation: Other functions may also create bool type.
End of explanation
empty = {}
empty
type(empty)
food = {'ham': 'yes',
       'egg': 'yes',
       'spam': 'no'}
food
food['ham']
food['spam'] = 'yes'
food
len(food)
# Accessing non Existing keys
food['apple']
# Merge dictionary
food2 = {'beef': 'yes',
        'shoe': 'no'}
food.update(food2)
food
# Iterating over Dictionary
for key in food:
    print(key)
    print(food[key])
    print('\n')
Explanation: Dict
Dict is another very important data structure in python
Comparing to list, it is a unordered sets or objects
Moreover, the item are accessed via keys and not via their position
End of explanation
N = 10
if N%2 == 0:
    print('Even')
else:
    print('Odd')
        
N = 9
if N%2 == 0:
    print('Even')
else:
    print('Odd')
N = 9
if N%2 == 0 and N > 10:
    print('A Even number greater than 10')
else:
    print('smaller than 10 or odd number')
N = 0
while N <= 10:
    if N%2 == 0:
        print(N, 'is Even.')
    else:
        print(N, ' is Odd.')
    N = N+1
Explanation: Conditional Statement
Conditional statement are used to execute code fragments based on a condition.
The most commonly used construct is if-else and while statement
End of explanation
# basic function
def add(x, y):
    return x+y
add(2, 3)
# function with optional parameters
def add(x, y=5):
    return x + y
add(3)
add(3, 9)
# Keyword Paramters
def add(x, y=5):
    return x + y
add(3, y=10)
def isEven(N):
    if N%2 == 0:
        return True
    else:
        return False
isEven(10)
isEven(9)
Explanation: Function
End of explanation
def productEven(l):
    ret = 1
    for item in l:
        if item % 2 == 0:
            ret = ret * item
    return ret
productEven([2, 3, 8, 7])
Explanation: Exercises 1
Please construct a function named productEven which imput a list of integers and return the product of the even numbers in the list.
For example:
pruductEven([2, 3, 8, 7]) gives 16
End of explanation
result_l = []
for i in range(2000, 3201):
    if i%7 == 0 and i%5 != 0:
        result_l.append(i)
result_l
Explanation: Exercises 2
Write a code which will find all such numbers which are divisible by 7 but are not a multiple of 5,
between 2000 and 3200 (both included).
End of explanation
l = [4, 2, 5, 6, 4]
count = 0
for item in l:
    if item == 4:
        count = count + 1
count
Explanation: Exercises 3
Write a python program to count the number 4 in a given list.
End of explanation
def gcd(a, b):
    for i in range(max(a, b)+1, 0, -1):
        if a%i == 0 and b%i == 0:
            return i
gcd(4, 6)
Explanation: Exercises 4
Write a Python program to compute the greatest common divisor (GCD) of two positive integers.
End of explanation
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