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Module 1: Optional Python review¶

Are you still new to Python? Or your python skill is a bit rusty?

Then, feel free to use this to learn or refresh Python basics! You don't have to submit this notebook. It is just for your own reference.

1. Built-in object types¶

1.1 Int and Float¶

In [ ]:

# Declaring an integer and a float variable
x = 10 
y = 3.0
k = x + y + 100

# Comments start with the hash symbol
# y = 10

# The value stored in the variable can be inspected by using print statement. 
# Type of a variable var can be checked by calling type(var) 
print("The value of x is", x, "and it is of type", type(x))

# f-strings can be used to write more elegant print statement. 
print(f"The value of y is {y} and it is of type {type(y)}")
print(f"The value of k is {k} and it is of type {type(k)}")

# casting int to float
print(f"x is of type {type(x)}")
x = float(x)
print(f"x is of type {type(x)} after casting")

# Declaring an integer and a float variable x = 10 y = 3.0 k = x + y + 100 # Comments start with the hash symbol # y = 10 # The value stored in the variable can be inspected by using print statement. # Type of a variable var can be checked by calling type(var) print("The value of x is", x, "and it is of type", type(x)) # f-strings can be used to write more elegant print statement. print(f"The value of y is {y} and it is of type {type(y)}") print(f"The value of k is {k} and it is of type {type(k)}") # casting int to float print(f"x is of type {type(x)}") x = float(x) print(f"x is of type {type(x)} after casting")

In [ ]:

# Arithmetic operators

# Addition
z = x + y
print(f"Adding x and y gives {z}")

# Subtraction
z = x - y
print(f"Subtracting y from x gives {z}")

# Multiplication
z = x * y
print(f"Multiplying x and y gives {z}")

# Division
z = x / y 
print(f"x divided by y gives {z}") 

# Floor Division
z = x // y 
print(f"x divided by y gives {z} as quotient") 

# Modulus Operator
z = x % y 
print(f"x divided by y gives {z} as reminder")

# Exponentiation
z = x ** y
print(f"x raised to y gives {z}") 

# self increment by 1
x = x + 1
# This is equivalent to x += 1
print(f"x + 1 gives {x}")

# Arithmetic operators # Addition z = x + y print(f"Adding x and y gives {z}") # Subtraction z = x - y print(f"Subtracting y from x gives {z}") # Multiplication z = x * y print(f"Multiplying x and y gives {z}") # Division z = x / y print(f"x divided by y gives {z}") # Floor Division z = x // y print(f"x divided by y gives {z} as quotient") # Modulus Operator z = x % y print(f"x divided by y gives {z} as reminder") # Exponentiation z = x ** y print(f"x raised to y gives {z}") # self increment by 1 x = x + 1 # This is equivalent to x += 1 print(f"x + 1 gives {x}")

1.2 Booleans and None¶

In [ ]:

# True and False are the key words that represent bool values in python
a = True
b = False

print(f"a is {a} and b is {b}")
print(f"Type of variable a and b is {type(a)}")

# None in python represents the absence of something; similar to null value
c = None 
print(f"c is {c} and is of type {type(c)}")

# Any non-zero integer value is true and zero is false.
# Also anything with a non-zero length is true and empty sequences are false.

# True and False are the key words that represent bool values in python a = True b = False print(f"a is {a} and b is {b}") print(f"Type of variable a and b is {type(a)}") # None in python represents the absence of something; similar to null value c = None print(f"c is {c} and is of type {type(c)}") # Any non-zero integer value is true and zero is false. # Also anything with a non-zero length is true and empty sequences are false.

In [ ]:

# logical operators 

# and, or and not operate on bool variables
# OR operator: Gives True when either of the expressions evaluates to True
# expr1 or expr2
print(f"a or b is {a or b}")
print(f"a or a is {a or a}")
print(f"b or b is {b or b}")

# AND operator: Gives True when both the expressions evaluates to True
# expr1 and expr2
print(f"a and b is {a and b}")
print(f"a and a is {a and a}")
print(f"b and b is {b and b}")

# NOT operator: negates a bool
# not expr1
print(f"Not of a is {not a}")

# logical operators # and, or and not operate on bool variables # OR operator: Gives True when either of the expressions evaluates to True # expr1 or expr2 print(f"a or b is {a or b}") print(f"a or a is {a or a}") print(f"b or b is {b or b}") # AND operator: Gives True when both the expressions evaluates to True # expr1 and expr2 print(f"a and b is {a and b}") print(f"a and a is {a and a}") print(f"b and b is {b and b}") # NOT operator: negates a bool # not expr1 print(f"Not of a is {not a}")

In [ ]:

# comparison operators

x = 10
y = 3.0
z = 5

# greater that, less than, greater than equal to and lesser than equal to
x > y
x >= y
x < y
x <= y

# equals and not equals
x == y
x != y

# Chained Expressions 
x > y > z 
(x > y) or (x > z)

# comparison operators x = 10 y = 3.0 z = 5 # greater that, less than, greater than equal to and lesser than equal to x > y x >= y x < y x <= y # equals and not equals x == y x != y # Chained Expressions x > y > z (x > y) or (x > z)

1.3 Strings¶

In [ ]:

# strings are represented using single or double quotes
first_name = "Adam" 
last_name = 'Eve'

# \ is used to escape characters
middle_name = 'zero\'s'

# string concatenation
full_name = first_name +' ' + middle_name + ' ' + last_name

print(f"Full name is {full_name}")
print(f"Full name is of type {type(full_name)}")

# strings can be indexed and sliced similar to lists and tuples. 
# List indexing is discussed in the list section

# strings are represented using single or double quotes first_name = "Adam" last_name = 'Eve' # \ is used to escape characters middle_name = 'zero\'s' # string concatenation full_name = first_name +' ' + middle_name + ' ' + last_name print(f"Full name is {full_name}") print(f"Full name is of type {type(full_name)}") # strings can be indexed and sliced similar to lists and tuples. # List indexing is discussed in the list section

In [ ]:

# casting str to int  
total = int('1') + int('2')
print(f"The value of total is {total} and it is of type {type(total)}")

# casting int to str
     
total = str(1) + str(2)
print(f"The value of total is {total} and it is of type {type(total)}")

# casting str to int total = int('1') + int('2') print(f"The value of total is {total} and it is of type {type(total)}") # casting int to str total = str(1) + str(2) print(f"The value of total is {total} and it is of type {type(total)}")

1.4 Lists and Tuples¶

In [ ]:

# Arrays are implemented as lists in python

# creating empty list
names = []
names = list()

# list of strings
names = ['Zach', 'Jay']
print(names)

# list of intergers
nums = [1, 2, 3, 4, 5]
print(nums)

# list of different data types
l = ['Zach', 1, True, None]
print(l)

# list of lists
ll = [[1, 3], [2, 3], [3, 4]]

# finding the length of list
length = len(l)
print(length)

# Arrays are implemented as lists in python # creating empty list names = [] names = list() # list of strings names = ['Zach', 'Jay'] print(names) # list of intergers nums = [1, 2, 3, 4, 5] print(nums) # list of different data types l = ['Zach', 1, True, None] print(l) # list of lists ll = [[1, 3], [2, 3], [3, 4]] # finding the length of list length = len(l) print(length)

In [ ]:

# Lists are mutable

names = names + ['Ravi']
names.append('Richard')
names.extend(['Abi', 'Kevin'])
print(names)

# Lists are mutable names = names + ['Ravi'] names.append('Richard') names.extend(['Abi', 'Kevin']) print(names)

In [ ]:

# List indexing and slicing
# an element or a subset of list can be accessed using element's index or slice of indices
# same notation applies for strings but at char level

# some_list[index]
# some_list[start_index: end_index(not included)]

numbers = [0, 1, 2, 3, 4, 5, 6]

# indices start from 0 in python
print(f'The first element in numbers is {numbers[0]}')
print(f'The third element in numbers is {numbers[2]}')

print(f'Elements from 1st to 5th index are {numbers[1:6]}')
print(f'Elements from start to 5th index are {numbers[:6]}')
print(f'Elements from 4th index to end are {numbers[4:]}')

print(f'Last Element is {numbers[-1]}')
print(f'Last four element are {numbers[-4:]}')

# changing 1st element in the numbers list
numbers[0] = 100
print(numbers)

# changing first 3 numbers
numbers[0: 3] = [100, 200, 300]
print(numbers)

# List indexing and slicing # an element or a subset of list can be accessed using element's index or slice of indices # same notation applies for strings but at char level # some_list[index] # some_list[start_index: end_index(not included)] numbers = [0, 1, 2, 3, 4, 5, 6] # indices start from 0 in python print(f'The first element in numbers is {numbers[0]}') print(f'The third element in numbers is {numbers[2]}') print(f'Elements from 1st to 5th index are {numbers[1:6]}') print(f'Elements from start to 5th index are {numbers[:6]}') print(f'Elements from 4th index to end are {numbers[4:]}') print(f'Last Element is {numbers[-1]}') print(f'Last four element are {numbers[-4:]}') # changing 1st element in the numbers list numbers[0] = 100 print(numbers) # changing first 3 numbers numbers[0: 3] = [100, 200, 300] print(numbers)

In [ ]:

# Tuples are immutable lists. They are created using () instead of [].

names = tuple()
names = ('Zach', 'Jay') 
print(names[0])

# trying to alter the tuple gives an error
names[0] = 'Richard'

# similar to tuples, strings are also immutable

# Tuples are immutable lists. They are created using () instead of []. names = tuple() names = ('Zach', 'Jay') print(names[0]) # trying to alter the tuple gives an error names[0] = 'Richard' # similar to tuples, strings are also immutable

1.5 Dictionary¶

In [ ]:

# hash maps in python are called Dictionaries
# dict{key: value}

# Empty dictionary
phonebook = dict()

# contruction dict using sequences of key-value pairs
dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])

# Dictionary with one item
phonebook = {'jack': 4098}

# Add another item
phonebook['guido'] = 4127

print(phonebook)
print(phonebook['jack'])
print(phonebook.items())
print(phonebook.keys())
print(phonebook.values())

print('jack' in phonebook)
print('Kevin' in phonebook)

# Delete an item
del phonebook['jack'] 
print(phonebook)

# hash maps in python are called Dictionaries # dict{key: value} # Empty dictionary phonebook = dict() # contruction dict using sequences of key-value pairs dict([('sape', 4139), ('guido', 4127), ('jack', 4098)]) # Dictionary with one item phonebook = {'jack': 4098} # Add another item phonebook['guido'] = 4127 print(phonebook) print(phonebook['jack']) print(phonebook.items()) print(phonebook.keys()) print(phonebook.values()) print('jack' in phonebook) print('Kevin' in phonebook) # Delete an item del phonebook['jack'] print(phonebook)

2. Flow control statements¶

2.1 if... elif... else...¶

In [ ]:

# if expr1:
#     code1
# elif expr2:
#     code2
#   .
#   .
#   .
#   .
# else:
#     code_n

# code1 is executed if expr1 is evaluated to true. Else it moves to expr2 and checks for true 
# condition and moves to the next if not true. 
# Finally if all the excpression's are false, code_n is executed

x = int(input("Please enter an integer: "))

if x < 0:
    x = 0
    print('Negative changed to zero')
elif x == 0:
    print('Zero')
elif x == 1:
    print('Single')
else:
    print('More')

# if expr1: # code1 # elif expr2: # code2 # . # . # . # . # else: # code_n # code1 is executed if expr1 is evaluated to true. Else it moves to expr2 and checks for true # condition and moves to the next if not true. # Finally if all the excpression's are false, code_n is executed x = int(input("Please enter an integer: ")) if x < 0: x = 0 print('Negative changed to zero') elif x == 0: print('Zero') elif x == 1: print('Single') else: print('More')

3. Loops¶

3.1 For loops¶

In [ ]:

# for loop is used to iter over any iterable object

# iterating over list
for name in ['Steve', 'Jill', 'Venus']:
    print(name)

# for loop is used to iter over any iterable object # iterating over list for name in ['Steve', 'Jill', 'Venus']: print(name)

In [ ]:

# iterating over string
for char in "Hellooooo":
    print(char)

# iterating over string for char in "Hellooooo": print(char)

In [ ]:

# iterating over dict keys
phone_nos = {"Henry": 6091237458,
             "James": 1234556789, 
             "Larry": 5698327549, 
             "Rocky": 8593876589}
for name, no in phone_nos.items():
    print(name, no)

# iterating over dict keys phone_nos = {"Henry": 6091237458, "James": 1234556789, "Larry": 5698327549, "Rocky": 8593876589} for name, no in phone_nos.items(): print(name, no)

In [ ]:

# To iterate over a sequence of numbers we use range() function. 
# range(start=0, end, step=1)
for i in range(2, 20, 2):
    print(i)

# To iterate over a sequence of numbers we use range() function. # range(start=0, end, step=1) for i in range(2, 20, 2): print(i)

In [ ]:

# using len of list/tuple in range
names = ['Steve', 'Rock', 'Harry']
for i in range(len(names)):
    print(names[i])

# using len of list/tuple in range names = ['Steve', 'Rock', 'Harry'] for i in range(len(names)): print(names[i])

3.2 While Loop¶

In [ ]:

# While loop executes as long as the condition remains true.
# while cond1:
#     pass

i = 0
while i < 10:
    print(i)
    i += 1

# While loop executes as long as the condition remains true. # while cond1: # pass i = 0 while i < 10: print(i) i += 1

In [ ]:

# Forever loop: The below code runs for ever

# while True:
#     print('Forever...')

# Forever loop: The below code runs for ever # while True: # print('Forever...')

3.3 Break, Continue and Pass statements¶

In [ ]:

# break statement breaks out of the the loop
while True:
    print('We’re stuck in a loop...')
    break # Break out of the while loop
print("not!")

# break statement breaks out of the the loop while True: print('We’re stuck in a loop...') break # Break out of the while loop print("not!")

In [ ]:

# continue statement skips a loop
for i in range(5):
    continue 
    print(i)

# continue statement skips a loop for i in range(5): continue print(i)

In [ ]:

# pass statement does nothing and is used as a placeholder
for i in range(10):
    pass

# pass statement does nothing and is used as a placeholder for i in range(10): pass

4. Importing Modules¶

In [ ]:

# importing modules using import statement
import math

# Import under an alias (avoid this pattern except with the most 
# common modules like pandas, numpy, etc.)
import math as m

# Access components with pkg.fn
m.pow(2, 3) 

# Import specific submodules/functions (not usually recommended 
# because it can be confusing to know where a function comes from)
from math import pow
pow(2, 3)

# importing modules using import statement import math # Import under an alias (avoid this pattern except with the most # common modules like pandas, numpy, etc.) import math as m # Access components with pkg.fn m.pow(2, 3) # Import specific submodules/functions (not usually recommended # because it can be confusing to know where a function comes from) from math import pow pow(2, 3)

5. Defining Functions¶

In [ ]:

# Functions in python are defined using key word "def"

# simple function to print greetings `greet_word` is an optional argument.
def greet(name, greet_word='Hello'):
    print(f"{greet_word} {name}. How are you doing?")

# here greet has 'Hello' as default argument for greet_word
print(greet('James'))
print(greet("Steven", greet_word="Howdy"))

# Observe that the function by default returns None

# Functions in python are defined using key word "def" # simple function to print greetings `greet_word` is an optional argument. def greet(name, greet_word='Hello'): print(f"{greet_word} {name}. How are you doing?") # here greet has 'Hello' as default argument for greet_word print(greet('James')) print(greet("Steven", greet_word="Howdy")) # Observe that the function by default returns None

In [ ]:

# Function to print nth fibonacci number
def fib(n):
    if n <= 1:
        return 1
    else:
        return fib(n-1)+fib(n-2)
n = 10
print(f"{n}th fibonacci number is {fib(n)}")

# Function to print nth fibonacci number def fib(n): if n <= 1: return 1 else: return fib(n-1)+fib(n-2) n = 10 print(f"{n}th fibonacci number is {fib(n)}")

Questions¶

For each of the following question, first think about the result without running the code. Then test it by running the code. Reach out if you don't understand why!

What's the output?¶

def func(a):
    a = a + 2
    a = a * 2
    return a
 
print(func(2))

In [ ]:

True? False? Why?¶

0.1 + 0.2 == 0.3

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

3. What is list_1 and list_2 and why?¶

list_1 = [1,2,3]
list_2 = list_1
list_1.append(4)
list_2 += [5]
list_2 = list_2 + [10]

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What's the output?¶

l = [i**2 for i in range(10)]
l[-4:2:-3]

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What does the code do? If the ordering doesn't matter, how can it be simplified?¶

def func1(lst):
    a = []
    for i in lst:
        if i not in a:
            a.append(i)
    return a

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What would be the output?¶

val = [0, 10, 15, 20]
data = 15
try:
    data = data/val[0]
except ZeroDivisionError:
    print("zero division error - 1")
except:
    print("zero division error - 2")
finally:
    print("zero division error - 3")

val = [0, 10, 15, 20]
data = 15
try:
    data = data/val[4]
except ZeroDivisionError:
    print("zero division error - 1")
except:
    print("zero division error - 2")
finally:
    print("zero division error - 3")

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What does the code do?¶

def func(s):
    d = {}
    for c in s:
        if c in d:
            d[n] += 1
        else:
            d[n] = 1
    return d

(Btw, the same operation can be done by simply running Counter(s) by using Counter data structure in the collections module.)

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What's the output?¶

def func(l):
    l.append(10)
    return l

a = [1,2,3]
b = func(a)
a == b

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What's happening to a in each step? Why?¶

# step 1
a = [ [ ] ] * 5
# step 2
a[0].append(10)
# step 3
a[1].append(20)
# step 4
a.append(30)

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What's the output?¶

L = list('abcdefghijk')
L[1] = L[4] = 'x'
L[3] = L[-3]
print(L)

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What's the output?¶

y = 8
z = lambda x : x * y
print (z(6))

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE

What's the output?¶

count = 1 

def func(count):
    for i in (1, 2, 3): 
        count += 1
func(count = 10)
count += 5
print(count)

In [ ]:

# YOUR SOLUTION HERE

# YOUR SOLUTION HERE