Python Programming

Class 3

Author: Jose Miguel Arrieta R.

Parentesis

Can you open power shell?

Tuples

Additional resource: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

A tuple is an (immutable) ordered list of values.

*see examples

# Create a tuple
t = (5, 6)

# Create a tuple
tuplex = 'tuple', False, 3.2, 1

Tuples Methods

Resource: https://www.programiz.com/python-programming/tuple

Only the following two methods are available.

*see more examples

my_tuple = ('a','p','p','l','e',)

# Count
# Output: 2
print(my_tuple.count('p'))

# Index
# Output: 3
print(my_tuple.index('l'))

Lists

A list is the Python equivalent of an array, but is resizable and can contain elements of different types

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

*see examples

xs = [3, 1, 2]    # Create a list

#See concatenate lists and methods

Lists slicing

Python provides concise syntax to access sublists; this is known as slicing

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

*see examples

nums = list(range(5))     # range is a built-in function that creates a list of integers
print(nums)               # Prints "[0, 1, 2, 3, 4]"
print(nums[2:4])          # Get a slice from index 2 to 4 (exclusive); prints "[2, 3]"

Lists Loops

animals = ['cat', 'dog', 'monkey']

"""
Loops: You can loop over 
the elements of a list like this
"""
for animal in animals:
    print(animal)

"""
If you want access to the index of each element within the body of a loop, 
use the built-in enumerate function
"""
for idx, animal in enumerate(animals):
    print(str(idx)+') ' +animal)

"""
Bad alternative from Java style developers, 
better use built in enumerate
"""
for i in range(0,len(animals))
	print(animal[i])

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

Tuples VS Lists

resources:

http://cs231n.github.io/python-numpy-tutorial/#python-tuples

http://www.diveintopython.net/native_data_types/tuples.html

https://docs.python.org/3/tutorial/datastructures.html

• Tuples are immutable, and usually contain a heterogeneous sequence of elements.
  • ​'faster' than lists
  • 'protect' the data
• Lists are mutable, and their elements are usually homogeneous
• You can't add elements to a tuple. Tuples have no append or extend method.
• You can't remove elements from a tuple. Tuples have no remove or pop method.
• You can know if element exists in tuple and in lists.

Sets

A set is an unordered collection with

no duplicate elements.

animals = {'cat', 'dog','cat','dog','turtle'}

*see examples

Dictionaries

A dictionary stores (key, value) pairs,

similar to a Map in Java or an object in Javascript.

resources: http://cs231n.github.io/python-numpy-tutorial/#python-tuples

# Create a new dictionary with some data
d = {'cat': 'cute', 'dog': 'furry'}

*see examples

Convert

1. dict to list
2. set to list
3. list to set

Exercise 1 [List] 

• Write a Python function named select_odds to select the odd items of a list.
• Note: function should result a list with result.

#Test cases 
>>> select_odds([24,30,44,55,12])
[55]
>>> select_odds([24,30,44,55,12,3,5,6])
[55, 3, 5]
>>>

Answer 1  

def select_odds(listA):
    odd_list = []
    for number in listA:
        if number%2 != 0:        
            odd_list.append(number)
    return odd_list

Exercise 2 [Lists] 

• Write function select_unique_values to get unique values from a list.
• Note: result should be in a list. 

#Test cases
>>> select_unique_values([2,2,2,2,3,3,1,2,6,7,8,9,9,10])
[1, 2, 3, 6, 7, 8, 9, 10]

>>> select_unique_values(['one','two','one','two','three','one'])
['three', 'two', 'one']

Answer 2  

def select_unique_values(listA): 
    return list(set(listA))

Exercise 3 [Dict] 

• Write  function sum_values to sum all the items in a dictionary.

#Test cases 

d = {'a': 3, 'b': 4,'c':5}

>>> sum_values(d)
12

Exercise 4 [Dict] 

• Write function get_max_min to get the maximum and minimum values in a dictionary and return result in form of tuple.
• Write function get_max_min_dict to get the maximum and minimum values in a dictionary and return result in form of dictionary.

>>> d = {'a': 3, 'b': 4,'c':50,'d':1}
>>> get_max_min(d)
(50, 1)
>>> get_max_min_dict(d)
{'max': 50, 'min': 1}

*Hint:

use max() and min() 

Answer 4  

def get_max_min(dictionary): 
	maximum = max(d.values())
	minimum = min(d.values())
	return maximum,minimum

def get_max_min_dict(dictionary): 
	maximum = max(d.values())
	minimum = min(d.values())
	return {'max':maximum,'min':minimum}