Week 5 Python Fundamental 2

Week 5: 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 [1]:

# Loop list
neighborhoods = ['Downtown Conway', 'Centennial Valley', 'West Conway']

for nei in neighborhoods:
    print(nei)

# Loop list neighborhoods = ['Downtown Conway', 'Centennial Valley', 'West Conway'] for nei in neighborhoods: print(nei)

Downtown Conway
Centennial Valley
West Conway

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 [5]:

conway = {
    'state': 'AR',
    'population': 64000,
    'gov_type': 'mayor_council'
}

conway = { 'state': 'AR', 'population': 64000, 'gov_type': 'mayor_council' }

In [ ]:

## get keys

## get keys

state
population
gov_type

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

In [ ]:

## get values

## get values

AR
64000
mayor_council

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

In [ ]:

## get items

## get items

state
population
gov_type

2. Conditionals: If...Elif...Else¶

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

In [10]:

cities = {
    'Little Rock': 202591,
    'Fort Smith': 89467,
    'Fayetteville': 99940,
    'Springdale': 84311
}

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

cities = { 'Little Rock': 202591, 'Fort Smith': 89467, 'Fayetteville': 99940, 'Springdale': 84311 } for city, pop in cities.items(): if pop > 200000: print('{} is a large city'.format(city))

Little Rock is a large city

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

hint: equal in Python is '=='

In [ ]:

89467

2.1 elif add the second contion in for loop¶

In [12]:

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))

Little Rock is a large city
Fort Smith is a small city
Fayetteville is a small city
Springdale is a small city

Source

3. Control Statements¶

3.1 Break, continue¶

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

In [3]:

for city, pop in cities.items():
    if pop > 85000:
        print('{} is a large city, population is {}'.format(city,pop))
        break

for city, pop in cities.items(): if pop > 85000: print('{} is a large city, population is {}'.format(city,pop)) break

Little Rock is a large city, population is 202591

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 [ ]:

Little Rock is a large city, population is 202591
Fort Smith is a large city, population is 89467
Fayetteville is a large city, population is 99940

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 [ ]:

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

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

In [14]:

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 [15]:

cities = {
    'Little Rock': 202591,
    'Fort Smith': 89467,
    'Fayetteville': 99940,
    'Springdale': 84311
}

find_large_city(cities,100000)

cities = { 'Little Rock': 202591, 'Fort Smith': 89467, 'Fayetteville': 99940, 'Springdale': 84311 } find_large_city(cities,100000)

Out[15]:

'Little Rock is a large city, population is 202591'

Exercise 6: User-defined function¶

Given a dictionary parks = {

'Cadron Settlement Park': 2006,

'Beaverfork Park': 1996,

'Laurel Park': 1921,

'Hendrix Creek Preserve': 2016

}, write a function to ouput the year of the park based on input as dictionary and park's name (string)

In [19]:

parks_dict = {
    'Cadron Settlement Park': 2006,
    'Beaverfork Park': 1996,
    'Laurel Park': 1921,
    'Hendrix Creek Preserve': 2016
}

parks_dict = { 'Cadron Settlement Park': 2006, 'Beaverfork Park': 1996, 'Laurel Park': 1921, 'Hendrix Creek Preserve': 2016 }

In [ ]:

In [21]:

find_park('Laurel Park', parks_dict)

find_park('Laurel Park', parks_dict)

Out[21]:

1921

In [22]:

find_park('Hendrix Creek Preserve', parks_dict)

find_park('Hendrix Creek Preserve', parks_dict)

Out[22]:

2016

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

In [23]:

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[23]:

'Both numbers are 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 [ ]:

Out[ ]:

'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 [26]:

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

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

9

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

In [27]:

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)

In [ ]:

from math import sin

from math import sin

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 [ ]:

from defined_math import substract_number, add_numbers

from defined_math import substract_number, add_numbers

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 [28]:

i = 1
while i <= 8:
  print(i)
  i += 1

i = 1 while i <= 8: print(i) i += 1

1
2
3
4
5
6
7
8

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 [ ]:

10
9
8
7
6
5
4
3
2
1
Time's up!

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 [30]:

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)

Please input a number2
okay, the number is 2

6.1 input and if¶

In [ ]:

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')

6.2 The break statement¶

With the break statement we can stop the while loop

In [ ]:

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

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 [ ]:

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

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

In [32]:

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('str')
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('str') print(rst_num)

Please input a valid number
The function is ended, and the result is listed below
None

In [33]:

print(calculate(6))

print(calculate(6))

The function is ended, and the result is listed below
2.0

Exercise 12¶

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

In [34]:

def divide_numbers(a, b):
    try:
        result = a / b
        return result
    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 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)
/tmp/ipython-input-2575125027.py in <cell line: 0>()
      7 
      8 # Example usage
----> 9 result_value = divide_numbers(10, 0)
     10 print(result_value)

/tmp/ipython-input-2575125027.py in divide_numbers(a, b)
      1 def divide_numbers(a, b):
      2     try:
----> 3         result = a / b
      4         return result
      5     finally:

ZeroDivisionError: division by zero

In [ ]:

Error: Division by zero is not allowed.
The function execution is complete.
None