Week 3 Python Fundamental 2

Week 3: Python Fundamental Part 2

1. Loops and Conditionals¶

1.1 For Loops¶

• A for loop can loop can interate over a sequence. The sequence can be a list, a string, or a dictionary

• 'indentation' is part of the loop's block, meaning it get executed every time the loop runs

In [2]:

# Loop list
neighborhoods = ['Indian Hill', 'Burncoat', 'Greendale']

for single_nei in neighborhoods:
    print(single_nei)

# Loop list neighborhoods = ['Indian Hill', 'Burncoat', 'Greendale'] for single_nei in neighborhoods: print(single_nei)

Indian Hill
Burncoat
Greendale

Exercise 1: Loop a dictionary¶

Please loop key, values and items seperately from a dictionary

worcester = {'state':'MA', 'population':206518, 'gov_type':'council_manager' }

• loop key

In [3]:

worcester = {'state':'MA',
             'population':206518,
             'gov_type':'council_manager'
             }

for i in worcester:
    print(i)

worcester = {'state':'MA', 'population':206518, 'gov_type':'council_manager' } for i in worcester: print(i)

state
population
gov_type

• loop values? (hint: how to get the values from dictionary?)

In [4]:

for i in worcester.values():
    print(i)

for i in worcester.values(): print(i)

MA
206518
council_manager

• loop items? (hint: how to get the items from dictionary?)

In [5]:

for all in worcester.items():
    print(all)

for all in worcester.items(): print(all)

('state', 'MA')
('population', 206518)
('gov_type', 'council_manager')

In [7]:

for values, keys in worcester.items():
    print(keys)

for values, keys in worcester.items(): print(keys)

MA
206518
council_manager

2. Conditionals: If...Elif...Else¶

if statement and loops is way to determine the condition and make decision.

In [12]:

cities = {'Boston':653833,
          'Worcester':207621,
          'Springfield':153672,
          'Cambridge':118214}

for city, pop in cities.items():
    # print(city)
    if pop > 200000:
        print('{} is a large city'.format(city))

cities = {'Boston':653833, 'Worcester':207621, 'Springfield':153672, 'Cambridge':118214} for city, pop in cities.items(): # print(city) if pop > 200000: print('{} is a large city'.format(city))

Boston is a large city
Worcester is a large city

Exercise 3: print the population if the city name is 'Boston'¶

hint: equal in Python is '=='

In [16]:

for city, pop in cities.items():
    # print(city)
    if city == 'Boston':
        print('{} population is {}'.format(city, pop))

for city, pop in cities.items(): # print(city) if city == 'Boston': print('{} population is {}'.format(city, pop))

Boston population is 653833

2.1 elif add the second contion in for loop¶

In [17]:

for city, pop in cities.items():
    if pop < 150000:
        print('{} is a small city'.format(city))
    elif pop > 200000:
        print('{} is a large city'.format(city))
    else:
        print('{} does not belong to any group'.format(city))

for city, pop in cities.items(): if pop < 150000: print('{} is a small city'.format(city)) elif pop > 200000: print('{} is a large city'.format(city)) else: print('{} does not belong to any group'.format(city))

Boston is a large city
Worcester is a large city
Springfield does not belong to any group
Cambridge is a small city

Source

3. Control Statements¶

3.1 Break, continue and pass¶

• Break stops the execution and exit out of it.
• Continue skip the current step and go to the next iteration

In [18]:

for city, pop in cities.items():
    if pop > 200000:
        print('{} is a large city, population is {}'.format(city,pop))
        break

for city, pop in cities.items(): if pop > 200000: print('{} is a large city, population is {}'.format(city,pop)) break

Boston is a large city, population is 653833

Exercise 4. Replace break with continue¶

Replace the break with continue to see the difference

You shoud get two results since the code will continue

In [28]:

for city, pop in cities.items():
        for i in range(1,3):
            if pop > 500:
                print('{} is a large city, population is {}'.format(city,pop))
                # i  = i+1
                # print(i)
                continue

for city, pop in cities.items(): for i in range(1,3): if pop > 500: print('{} is a large city, population is {}'.format(city,pop)) # i = i+1 # print(i) continue

Boston is a large city, population is 653833
Boston is a large city, population is 653833
Worcester is a large city, population is 207621
Worcester is a large city, population is 207621
Springfield is a large city, population is 153672
Springfield is a large city, population is 153672
Cambridge is a large city, population is 118214
Cambridge is a large city, population is 118214

4. Functions¶

A function takes one or more inputs and return one of more outputs

The code wihitn the function runs only when it is called

In [25]:

# def funtion_name(input):
#    ...
#    return outputs

# def funtion_name(input): # ... # return outputs

In [30]:

def find_large_city(input_dict, population_num):
    for city,pop in input_dict.items():
        if pop > population_num:
            return '{} is a large city, population is {}'.format(city,pop)

def find_large_city(input_dict, population_num): for city,pop in input_dict.items(): if pop > population_num: return '{} is a large city, population is {}'.format(city,pop)

In [35]:

cities = {'Boston':653833,
          'Worcester':207621,
          'Springfield':153672,
          'Cambridge':118214}

find_large_city(cities,500)

cities = {'Boston':653833, 'Worcester':207621, 'Springfield':153672, 'Cambridge':118214} find_large_city(cities,500)

Out[35]:

'Boston is a large city, population is 653833'

Exercise 5: User-defined function¶

Previous function only return one result as soon as it finds the first city with a population greater than the specified number.

If you want it to return all citie that meet the criteria, you can modify the function to collect all matching cities and return them.

• create a empty list inside the function
• append each result to the list

In [39]:

def find_large_city(input_dict, population_num):
    # empty list
    newlist = []
    for city,pop in input_dict.items():
        if pop > population_num:
            # append city to list
            newlist.append(city)
            # return '{} is a large city, population is {}'.format(city,pop)
    return newlist

find_large_city(cities,500)

def find_large_city(input_dict, population_num): # empty list newlist = [] for city,pop in input_dict.items(): if pop > population_num: # append city to list newlist.append(city) # return '{} is a large city, population is {}'.format(city,pop) return newlist find_large_city(cities,500)

Out[39]:

['Boston', 'Worcester', 'Springfield', 'Cambridge']

Exercise 6: User-defined function¶

Given a dictionary parks = { 'Green hill':1875, 'Elm': 1854, 'Institute': 1887, 'Salisbury': 1887 }, write a function to ouput the year of the park based on input as dictionary and park's name (string)

In [ ]:

parks = {
    'Green hill':1875,
    'Elm': 1854,
    'Institute': 1887,
    'Salisbury': 1887
}

parks = { 'Green hill':1875, 'Elm': 1854, 'Institute': 1887, 'Salisbury': 1887 }

4.1 and and or are logical operators used to combine multiple conditions.

In [41]:

def check_numbers(a, b):
    if a > 0 and b > 0:
        return "Both numbers are positive."
    elif a > 0 or b > 0:
        return "At least one number is positive."
    else:
        return "Neither number is positive."

check_numbers(5,-3)

def check_numbers(a, b): if a > 0 and b > 0: return "Both numbers are positive." elif a > 0 or b > 0: return "At least one number is positive." else: return "Neither number is positive." check_numbers(5,-3)

Out[41]:

'At least one number is positive.'

Exercise 7: User-defined function¶

You can set up initial values for the arguments in the check_numbers function by providing defautl values in the fucntion definition.

In [44]:

def check_numbers(a=0, b=0):
    if a > 0 and b > 0:
        return "Both numbers are positive."
    elif a > 0 or b > 0:
        return "At least one number is positive."
    else:
        return "Neither number is positive."

check_numbers(a=3)

def check_numbers(a=0, b=0): if a > 0 and b > 0: return "Both numbers are positive." elif a > 0 or b > 0: return "At least one number is positive." else: return "Neither number is positive." check_numbers(a=3)

Out[44]:

'At least one number is positive.'

5. Module¶

Module is a folder that contain a set of functions you want to include in your applications

Using the import statement to use the module

Build-in modules are pre-installed with the Python installation.

random module¶

random module in Python provides functions for generating random numbers

• randint() function return a random integer between a and b: random.randint(a,b)

In [1]:

import random
num = randint(0,10)
print(num)

import random num = randint(0,10) print(num)

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Cell In[1], line 2
      1 import random
----> 2 num = randint(0,10)
      3 print(num)

NameError: name 'randint' is not defined

if you want to use randint() directly without the random prefix. You can import the function specifically like this

In [47]:

from random import randint
number = randint(1,10)
print(number)

from random import randint number = randint(1,10) print(number)

3

Exercise 8: Get the sine of a number from math module¶

• import math module
• use sin() function in math module to calculate sin(3)

Exercie 9. Writing and Using Python Modules¶

1. Creating a module is simple:

• Write your Python code in a .py file.
• Save the file with a meaningful name.

2. Write function in the module

3. Import function from the module

In [6]:

import defined_math

defined_math.add_numbers(7,9)

import defined_math defined_math.add_numbers(7,9)

Out[6]:

16

In [7]:

import math_function

math_function.divide(4,2)

import math_function math_function.divide(4,2)

Out[7]:

2.0

6. While loop¶

With the while loop we can execute a set of statements as long as a condition(or expression) is true

Below example is to show the while loop generate a list of numbers but remember that to increase i, or else the loop will continue forever

While expression:

  statements

In [9]:

i = 1
while i <= 5:
  print(i)
  i += 1

i = 1 while i <= 5: print(i) i += 1

1
2
3
4
5

Source

Exercie 11：Counting Down Timer¶

Let the while counts down from 10 to 1. When countdown reaches 0, the loop stops, and a message is printed

In [12]:

i = 10
while i >= 0:
  print(i)
  i -= 1

i = 10 while i >= 0: print(i) i -= 1

10
9
8
7
6
5
4
3
2
1
0

6. User input¶

input() function get user input, and converting that input from a string to an integer

Syntax:

input(prompt) prompt: a string, representing a message before the input

In [14]:

get_name = input("Please input a number")
print("okay, the number is " + get_name)

get_name = input("Please input a number") print("okay, the number is " + get_name)

okay, the number is 10

6.1 input and if¶

In [16]:

get_num = int(input("Please input a number"))

if get_num <= 5:
    print('Your number is smaller than 5')
else: 
    print('Your number is larger than 5')

get_num = int(input("Please input a number")) if get_num <= 5: print('Your number is smaller than 5') else: print('Your number is larger than 5')

Your number is smaller than 5

Exercise 12: Guess the Secret Number¶

Write a python program that generates a random number between 1 and 20. The program will then repeatedly prompt the user to guess the number. The loop will continue until the user guesses the correct number.

In [19]:

import random

# 1. generate a random integer number between 1 and 20
import random
get_random_num = random.randint(1,20)
selected_num = None

# 2. use a while loop to keep asking the user for guesses
while selected_num != get_random_num:
    # 3. use input function to get the input number
    selected_num = int(input("Please input a number"))
    # 4. After each incorrect guess, tell the user whether their guess was too high or too low: using if condition
    if selected_num < get_random_num:
        print('Your guessed number is lower')
    elif selected_num > get_random_num:
        print("Your guessed number is higher")
    else:
        print("Congrats! Your number is correct!")

import random # 1. generate a random integer number between 1 and 20 import random get_random_num = random.randint(1,20) selected_num = None # 2. use a while loop to keep asking the user for guesses while selected_num != get_random_num: # 3. use input function to get the input number selected_num = int(input("Please input a number")) # 4. After each incorrect guess, tell the user whether their guess was too high or too low: using if condition if selected_num < get_random_num: print('Your guessed number is lower') elif selected_num > get_random_num: print("Your guessed number is higher") else: print("Congrats! Your number is correct!")

Your guessed number is higher
Your guessed number is lower
Your guessed number is lower
Your guessed number is lower
Congrats! Your number is correct!

6.2 The break statement¶

With the break statement we can stop the while loop

In [20]:

i = 1
while i < 8:
  print(i)
  i += 1
  if i == 3:
    break

i = 1 while i < 8: print(i) i += 1 if i == 3: break

1
2

7. Error Handing exception¶

Error is the common issue in your code, how your responds to these errors, called exceptions.

• try | except | finally
  • try statement is used to process a block of code
  • except is used to catch the error
  • finally always run the code regardless of whether an exception occurred, providing feedback that the process is complete

In [21]:

def calculate(num):
    rst = num/3
    print(rst)
    
calculate('str')

def calculate(num): rst = num/3 print(rst) calculate('str')

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[21], line 4
      2     rst = num/3
      3     print(rst)
----> 4 calculate('str')

Cell In[21], line 2, in calculate(num)
      1 def calculate(num):
----> 2     rst = num/3
      3     print(rst)

TypeError: unsupported operand type(s) for /: 'str' and 'int'

In [23]:

def calculate(num):
    try: 
        rst = num/3
        return rst
    except TypeError:
        print('Please input a valid number')
    finally:
        print("The function is ended, and the result is listed below")

rst_num = calculate(3)
print(rst_num)

def calculate(num): try: rst = num/3 return rst except TypeError: print('Please input a valid number') finally: print("The function is ended, and the result is listed below") rst_num = calculate(3) print(rst_num)

The function is ended, and the result is listed below
1.0

In [ ]:

print(calculate(6))

print(calculate(6))

Exercise 13¶

The function below is about devide two number. But it raise a 'ZeroDevisionError'. Please modify the function to handle the error.

In [26]:

def divide_numbers(a, b):
    try:
        result = a / b
        return result
    # except ZeroDivisionError:
    #     print('no zero for b')
    finally:
        print("The function execution is complete.")

# Example usage
result_value = divide_numbers(10, 0)
print(result_value)

def divide_numbers(a, b): try: result = a / b return result # except ZeroDivisionError: # print('no zero for b') finally: print("The function execution is complete.") # Example usage result_value = divide_numbers(10, 0) print(result_value)

The function execution is complete.

---------------------------------------------------------------------------
ZeroDivisionError                         Traceback (most recent call last)
Cell In[26], line 11
      8         print("The function execution is complete.")
     10 # Example usage
---> 11 result_value = divide_numbers(10, 0)
     12 print(result_value)

Cell In[26], line 3, in divide_numbers(a, b)
      1 def divide_numbers(a, b):
      2     try:
----> 3         result = a / b
      4         return result
      5     # except ZeroDivisionError:
      6     #     print('no zero for b')
      7     finally:

ZeroDivisionError: division by zero

Exercise 14: Understanding if name == "main": in module¶

The special construct if name == "main" is used for:

• Imported as a module in another script.
• Determine whether a script is being run as the main program

In [27]:

# Imported as a module in another script. 

import print_number

print_number.numbers()

# Imported as a module in another script. import print_number print_number.numbers()

5

In [ ]:

# Run the script directly in terminal

# Run the script directly in terminal