PythonDataTypes

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Author Michael Robinson

Course Python

Topic dataTypes

Program dataTypes.py

Running/Executing Python programs:
- Windows terminal mode python dataTypes.py
- Linux terminal mode python dataTypes.py
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In python the hash or pound sign # is the beginnng of a single line comment.
There are no multi-line comments commands in Python.

In Python, it is not necessary to explicitly declare the data type of a
variable when creating it.

Python is a dynamically typed language, meaning the interpreter
infers the type of a variable at runtime based on the assigned value.
When assigning an integer value to a variable, the int type is
automatically assumed.

Python has the following data types built-in by default:

Numeric Data Types
------------------

int Represents integer numbers.

float Represents floating-point numbers (decimal numbers).

complex Represents complex numbers.

int integer data types examples
-------------------------------

first = 999 # x is automatically assumed as an integer

second = -99 # y is also an integer

third = 5431292363456734890 # Python integers can be arbitrarily large

print("\nThe following data types are ints also known as integers")
print("--------------------------------------------------------")
print("first = ", first)
print("second = ", second)
print("third = ", third)

print("\nThe data types of the previous numbers are")
print("------------------------------------------")
print( "The data type of first is ", type(first ))
print( "The data type of second is ", type(second))
print( "The data type of third is ", type(third ))

float data types examples
-------------------------
Python uses a single floating-point type, float, which is implemented as
a double-precision (64-bit) floating-point number.
In practice, the float type serves the purpose of both float and double
found in other languages.

gpa = 4.00 # gpa is automatically recognized as a float variable

height = 5.9 # height is automatically recognized as a float variable

weight = 189.6 # weight is automatically recognized as a float variable

print("\n\nThe following data types are floats")
print("-------------------------------------")
print( "gpa = ", gpa)
print( "height = ", height, "feet")
print( "weight = ", weight, "pounds")

print("\nThe data types of the previous numbers are")
print("------------------------------------------")
print( "The data type of gpa is ", type(gpa ))
print( "The data type of height is ", type(height))
print( "The data type of weight is ", type(weight))

complex numeric data types examples
-----------------------------------
Complex Numbers: Numbers with a real and an imaginary part,
denoted in the form a + bj, where:
a is the real part,
b is the imaginary part, and
j represents the square root of -1.

These complex data types provide flexibility and structure for storing and
processing data in Python, making them essential for a wide range of programming tasks.

print("\n\nThe following data types are named complex")
print("--------------------------------------------\n")

myComplexNumber = 2 + 3j

print( "myComplexNumber = ", myComplexNumber )

print( "The data type of myComplexNumber is ", type(myComplexNumber))

Results:
myComplexNumber = (2+3j)
The data type of myComplexNumber is <class 'complex'>
myComplexNumber = (2+3j) complex numeric data types examples
The data type of myComplexNumber is <class 'complex'>

str data types examples
-----------------------
str also known as text data type, represents strings (text).

The str data type accepts/contains alphabetic letters, spaces,
numbers and/or symbols such as &,*,@ etc.

myFirstName = "Michael" #automatically recognized as a str
myLastName = "Robinson" #automatically recognized as a str
myFullName = "Michael Robinson" #automatically recognized as a str
myAddress = "123 Main Avenue, Jefferson, NY, 11011" #recognized as a str

print("\n\nThe following data types are known as str")
print("-----------------------------------------")
print( "myFirstName = ", myFirstName )
print( "myLastName = ", myLastName )
print( "myFullName = ", myFullName )
print( "myAddress = ", myAddress )

print("\nThe data types of the previous variables are")
print("--------------------------------------------")
print( "The data type of myFirstName is ", type(myFirstName) )
print( "The data type of myLastName is ", type(myLastName) )
print( "The data type of myFullName is ", type(myFullName) )
print( "The data type of myAddress is ", type(myAddress) )

Boolean data types examples
---------------------------
bool Represents boolean values (True or False).

print("\n\nThe following data types are known as boolean")
print("---------------------------------------------")

print("Python has the usual boolean values used by all languages")
print("\nWhen we compare 2 or more items, if they are equivalent then the
answer is True")
print( "The symbol == means equivalent" )

a = 3
b = 3

print( "a = ", a )
print( "b = ", b )

print( "if we say a == b then the answer is", (a == b) )
print( "if we say a < b then the answer is", (a < b) )

print("\nThe data types of the previous variables are")
print("--------------------------------------------")

print( "The data type of (a == b) is ", type(a == b) )
print( "The data type of (a < b) is ", type(a < b) )

Primitive Data Types
--------------------
The following four data types are also known as Primitive Data Types

int Represents integer numbers. For example: 99, -156, 1020345867789456

float Represents floating-point numbers. For example: 3.12345, -0.999, 4.00

str Represents strings, which are sequences of characters. For example: '!!Life is good', "Python is great!!".

bool Represents boolean values, which can be either True or False

Sequence data types
-------------------

list Represents ordered, mutable sequences of items.

tuple Represents ordered, immutable sequences of items.

range Represents a sequence of numbers, often used in loops.

List data types examples
------------------------

list Represents ordered, *mutable* sequences of items.

mutable Allows to change, add or remove data in a data structure.

Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.

Lists are used to store multiple items in a single variable and each item in a specific location/index in the list.

Lists are created using square brackets.

In the following example I am creating a list named mylist containing 3 data items:

mylist = ["Orlando", "Michael", "Pilar"]

mylist list contains three items Orlando, Michael and Pilar
Orlando is located in index myList[0]
Michael is located in index myList[1]
Pilar is located in index myList[2]

Printing my entire mylist list:

print(mylist)

Results:
["Orlando", "Michael", "Pilar"]

adding the item Ivan to mylist at the third location/index
**notice that the third location/index is [4] because we start at location/index [0]

mylist.insert( 4, "Ivan")

print(mylist)

Results:
["Orlando", "Michael", "Pilar", "Ivan"]

Allow Duplicates
----------------
Lists allow duplicate values:

copy data in location/index 0 to location/index 4

mylist.insert( 5, "Orlando") #this inserts Orlando into location/index 5

print(mylist)

Results:
["Orlando", "Michael", "Pilar", "Ivan", "Orlando"]

Since lists are indexed, lists can have items with the same value.

Override variables values
-------------------------
insert the value Zero into location/index 0 #this overides value Orlando in location/index 0 with value Zero
mylist.insert( 0, "Zero") #this overrides the value location/index in location/index 0

print(mylist)

Results:
["Zero", "Michael", "Pilar", "Ivan", "Orlando"]

List Items
----------
List items are ordered, changeable, and allow duplicate values.
List items are indexed, the first item has index [0], the second item has index [1] etc.

Ordered
-------
When we say that lists are ordered, it means that the items have a defined order, and that order will not change.

If you add new items to a list, the new items will be placed at the end of the list.

mylist.append( "Vidita" )

print(mylist)

Results:
["Zero", "Michael", "Pilar", "Ivan", "Orlando", "Vidita"]

Note: There are some list methods that will change the order, but in general: the order of the items will not change.

Changeable
----------
The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.

List Length
-----------
To determine how many items a list has, use the len() function:

Print the number of items in the list:
thislist = ["Zero", "Michael", "Pilar", "Ivan", "Orlando", "Vidita"]

print( "This list has ", len(thislist), "variables" )

Results:
This list has 6 variables.

List Items - Data Types
-----------------------
List items can be of any data type:

String, int and boolean data types:
list1 = ["Orlando", "Michael", "Pilar"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]

A list can contain different data types:
A list with strings, integers and boolean values:
list1 = ["abc", 34, True, 40, "male"]

type()
------
From Python's perspective, lists are defined as objects with the data type 'list':

What is the data type of a list?
mylist = ["Orlando", "Michael", "Pilar"]
print(type(mylist))

*HERE

The list() Constructor
-----------------------
It is also possible to use the list() constructor when creating a new list.
Using the list() constructor to make a List:
thislist = list(("Orlando", "Michael", "Pilar")) # note the double round-brackets
print(thislist)

Python Collections (Arrays)
---------------------------
There are four collection data types in the Python programming language:
- List is a collection which is ordered and changeable. Allows duplicate members.

- Tuple is a collection which is ordered and unchangeable. Allows duplicate members.

- Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.

- Dictionary is a collection which is ordered** and changeable.

No duplicate members.
*Set items are unchangeable, but you can remove and/or add items whenever you like.

**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

Access List Items
-----------------
List items are indexed and you can access them by referring to the index number:
Print the second item of the list:

thislist = ["Orlando", "Michael", "Pilar"]
print(thislist[1])
Note: The first item has index 0.

Negative Indexing
Negative indexing means start from the end

-1 refers to the last item, -2 refers to the second last item etc.

Print the last item of the list:

thislist = ["Orlando", "Michael", "Pilar"]
print(thislist[-1])
Range of Indexes
You can specify a range of indexes by specifying where to start and where to end the range.

When specifying a range, the return value will be a new list with the specified items.

Return the third, fourth, and fifth item:

thislist = ["Orlando", "Michael", "Pilar", "Martha", "Jackie", "Nidia", "Harold"]
print(thislist[2:5])
Note: The search will start at index 2 (included) and end at index 5 (not included)
.
Remember that the first item has index 0.

By leaving out the start value, the range will start at the first item:

This returns the items from the beginning to, but NOT including, "Jackie":

thislist = ["Orlando", "Michael", "Pilar", "Martha", "Jackie", "Nidia", "Harold"]
print(thislist[:4])
By leaving out the end value, the range will go on to the end of the list:

This returns the items from "Pilar" to the end:

thislist = ["Orlando", "Michael", "Pilar", "Martha", "Jackie", "Nidia", "Harold"]
print(thislist[2:])
Range of Negative Indexes
Specify negative indexes if you want to start the search from the end of the list:

This returns the items from "Martha" (-4) to, but NOT including "Harold" (-1):

thislist = ["Orlando", "Michael", "Pilar", "Martha", "Jackie", "Nidia", "Harold"]
print(thislist[-4:-1])
Check if Item Exists
To determine if a specified item is present in a list use the in keyword:

Check if "Orlando" is present in the list:

thislist = ["Orlando", "Michael", "Pilar"]
if "Orlando" in thislist:
print("Yes, 'Orlando' is in the friends list")

-------
What will be the result of the following syntax:
mylist = ['Orlando', 'Michael', 'Pilar']
print(mylist[-1])

Orlando
Michael
Pilar

Change List Items
-----------------
Change Item Value
To change the value of a specific item, refer to the index number:

Change the second item:

thislist = ["Orlando", "Michael", "Pilar"]
thislist[1] = "blackcurrant"
print(thislist)
Change a Range of Item Values
To change the value of items within a specific range, define a list with the new values, and refer to the range of index numbers where you want to insert the new values:

Change the values "Michael" and "Pilar" with the values "blackcurrant" and "Nidia":

thislist = ["Orlando", "Michael", "Pilar", "Martha", "Jackie", "Harold"]
thislist[1:3] = ["blackcurrant", "Nidia"]
print(thislist)
If you insert more items than you replace, the new items will be inserted where you specified, and the remaining items will move accordingly:

Change the second value by replacing it with two new values:

thislist = ["Orlando", "Michael", "Pilar"]
thislist[1:2] = ["blackcurrant", "Nidia"]
print(thislist)
Note: The length of the list will change when the number of items inserted does not match the number of items replaced.

If you insert less items than you replace, the new items will be inserted where you specified, and the remaining items will move accordingly:

Change the second and third value by replacing it with one value:

thislist = ["Orlando", "Michael", "Pilar"]
thislist[1:3] = ["Nidia"]
print(thislist)

Insert Items
------------
The insert() method inserts an item at the specified index
Insert "Nidia" as the third item:

thislist = ["Orlando", "Michael", "Pilar"]
thislist.insert(2, "Nidia")
print(thislist)

Note: As a result of the above, the list will now contain 4 items.

What will be the result of the following syntax:
mylist = ['Orlando', 'Michael', 'Pilar']
mylist[0] = 'Jackie'
print(mylist[1])

Jackie
Orlando
Michael
Pilar

Append List Items
-----------------
To add an item to the end of the list, use the append() method:

Using the append() method to append an item:

thislist = ["Orlando", "Michael", "Pilar"]
thislist.append("Martha")
print(thislist)

**here

Insert Items
------------
To insert a list item at a specified index, use the insert() method.

The insert() method inserts an item at the specified index:

Insert an item as the second position
-------------------------------------
thislist = ["Orlando", "Michael", "Pilar"]
thislist.insert(1, "Martha")
print(thislist)

Note: As a result of the s above, the lists will now contain 4 items.

Extend List
-----------
To append elements from another list to the current list, use the extend() method.

Add the elements of tropical to thislist:

thislist = ["Orlando", "Michael", "Pilar"]
tropical = ["Harold", "Andrea", "Panera"]
thislist.extend(tropical)
print(thislist)

The elements will be added to the end of the list.

Add Any Iterable
----------------
The extend() method does not have to append lists, you can add any iterable object (tuples, sets, dictionaries etc.).

Add elements of a tuple to a list:

thislist = ["Orlando", "Michael", "Pilar"]
thistuple = ("Jackie", "Martha")
thislist.extend(thistuple)
print(thislist)

Exercise
--------
What will be the result of the following syntax:
mylist = ['Orlando', 'Michael', 'Pilar']
mylist.insert(0, 'Martha')
print(mylist[1])

Orlando
Michael
Pilar
Martha

**here

Remove List Items
-----------------
Remove Specified Item
The remove() method removes the specified item.

Remove "Michael":

thislist = ["Orlando", "Michael", "Pilar"]
thislist.remove("Michael")
print(thislist)
If there are more than one item with the specified value, the remove() method removes the first occurrence:

Remove the first occurrence of "Michael"
----------------------------------------
thislist = ["Orlando", "Michael", "Pilar", "Michael", "Jackie"]
thislist.remove("Michael")
print(thislist)

Remove Specified Index
----------------------
The pop() method removes the specified index.

Remove the second item
----------------------
thislist = ["Orlando", "Michael", "Pilar"]
thislist.pop(1)
print(thislist)
If you do not specify the index, the pop() method removes the last item.

Remove the last item
--------------------
thislist = ["Orlando", "Michael", "Pilar"]
thislist.pop()
print(thislist)
The del keyword also removes the specified index:

Remove the first item
---------------------
thislist = ["Orlando", "Michael", "Pilar"]
del thislist[0]
print(thislist)

The del keyword can also delete the list completely.

Delete the entire list
----------------------
thislist = ["Orlando", "Michael", "Pilar"]
del thislist

Clear the List
--------------
The clear() method empties the list.
The list still remains, but it has no content.

Clear the list content
----------------------
thislist = ["Orlando", "Michael", "Pilar"]
thislist.clear()
print(thislist)

List methods for removing list items
------------------------------------
pop()
push()
delete()

Loop Through a List
-------------------
You can loop through the list items by using a for loop:

Print all items in the list, one by one
---------------------------------------
thislist = ["Orlando", "Michael", "Pilar"]
for x in thislist:
print(x)

Learn more about for loops in our Python For Loops Chapter.

Loop Through the Index Numbers
------------------------------
You can also loop through the list items by referring to their index number.
Use the range() and len() functions to create a suitable iterable.

Print all items by referring to their index number
--------------------------------------------------
thislist = ["Orlando", "Michael", "Pilar"]
for i in range(len(thislist)):
print(thislist[i])

The iterable created in the above is [0, 1, 2].

**here

Using a While Loop
------------------
You can loop through the list items by using a while loop.

Use the len() function to determine the length of the list, then start at 0 and loop your way through the list items by referring to their indexes.
Remember to increase the index by 1 after each iteration.
Print all items, using a while loop to go through all the index numbers

thislist = ["Orlando", "Michael", "Pilar"]

i = 0

while i < len(thislist):
print(thislist[i])
i = i + 1

Learn more about while loops in our Python While Loops Chapter.

Looping Using List Comprehension
List Comprehension offers the shortest syntax for looping through lists:

A short hand for loop that will print all items in a list:

thislist = ["Orlando", "Michael", "Pilar"]
[print(x) for x in thislist]
Learn more about list comprehension in the next chapter: List Comprehension.

Exercise
What is a correct syntax for looping through the items of a list?

for x in ['Orlando', 'Michael', 'Pilar']:
print(x)
for x in ['Orlando', 'Michael', 'Pilar']
print(x)
foreach x in ['Orlando', 'Michael', 'Pilar']
print(x)

List Comprehension
------------------
List Comprehension
List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.

Based on a list of friends, you want a new list, containing only the friends with the letter "a" in the name.

Without list comprehension you will have to write a for statement with a conditional test inside:

friends = ["Orlando", "Michael", "Pilar", "Jackie", "Harold"]
newlist = []

for x in friends:
if "a" in x:
newlist.append(x)

print(newlist)
With list comprehension you can do all that with only one line of code:
friends = ["Orlando", "Michael", "Pilar", "Jackie", "Harold"]

+ newlist = [x for x in friends if "a" in x]

print(newlist)

The Syntax
newlist = [expression for item in iterable if condition == True]
The return value is a new list, leaving the old list unchanged.

Condition
The condition is like a filter that only accepts the items that evaluate to True.

Only accept items that are not "Orlando":

newlist = [x for x in friends if x != "Orlando"]
The condition if x != "Orlando" will return True for all elements other than "Orlando", making the new list contain all friends except "Orlando".

The condition is optional and can be omitted:
With no if statement:
newlist = [x for x in friends]

Iterable
The iterable can be any iterable object, like a list, tuple, set etc.

You can use the range() function to create an iterable:

newlist = [x for x in range(10)]
Same , but with a condition:

Accept only numbers lower than 5:

newlist = [x for x in range(10) if [ x < 5]

Expression
The expression is the current item in the iteration, but it is also the outcome, which you can manipulate before it ends up like a list item in the new list:

Set the values in the new list to upper case:

newlist = [x.upper() for x in friends]

You can set the outcome to whatever you like:

Set all values in the new list to 'hello':
newlist = ['hello' for x in friends]
The expression can also contain conditions, not like a filter, but as a way to manipulate the outcome:

Return "Martha" instead of "Michael":

newlist = [x if x != "Michael" else "Martha" for x in friends]
The expression in the above says:
"Return the item if it is not Michael, if it is Michael return Martha".

Exercise
Consider the following code:
friends = ['Orlando', 'Michael', 'Pilar']
newlist = [x for x in friends if x == 'Michael']

What will be the value of newlist?
['Orlando', 'Pilar']
['Michael']

**here

Sort Lists
-------------------
Sort List Alphanumerically
List objects have a sort() method that will sort the list alphanumerically, ascending, by default:
Sort a list alphabetically:
---------------------------
thislist = ["Martha", "Harold", "Jackie", "Andrea", "Michael"]
thislist.sort()
print(thislist)

Sort a list numerically
-----------------------
thislist = [100, 50, 65, 82, 23]
thislist.sort()
print(thislist)

Sort a list descending
----------------------
thislist = ["Martha", "Harold", "Jackie", "Andrea", "Michael"]
thislist.sort(reverse = True)
print(thislist)

Sort the list descending
------------------------
thislist = [100, 50, 65, 82, 23]
thislist.sort(reverse = True)
print(thislist)

Customize Sort Function
-----------------------
You can also customize your own function by using the keyword argument key = function.

The function will return a number that will be used to sort the list (the lowest number first):

Sort the list based on how close the number is to 50:

def myfunc(n):
return abs(n - 50)

thislist = [100, 50, 65, 82, 23]
thislist.sort(key = myfunc)
print(thislist)

Case Insensitive Sort
---------------------
By default the sort() method is case sensitive, resulting in all upper case letters being sorted before lower case letters:

Case sensitive sorting can give an unexpected result:

thislist = ["Michael", "Martha", "Jackie", "Pilar"]
thislist.sort()
print(thislist)

Luckily we can use built-in functions as key functions when sorting a list.

So if you want a case-insensitive sort function, use str.lower as a key function:

Perform a case-insensitive sort of the list:
thislist = ["Michael", "Martha", "Jackie", "Pilar"]
thislist.sort(key = str.lower)
print(thislist)
Reverse Order
What if you want to reverse the order of a list, regardless of the alphabet?

The reverse() method reverses the current sorting order of the elements.

Reverse the order of the list items:

thislist = ["Michael", "Martha", "Jackie", "Pilar"]
thislist.reverse()
print(thislist)

Exercise
What is a correct syntax for sorting a list?

mylist.orderby(0)
mylist.order()
mylist.sort()

Copy Lists
----------
Copy a List
You cannot copy a list simply by typing list2 = list1, because: list2 will only be a reference to list1, and changes made in list1 will automatically also be made in list2.

Use the copy() method
You can use the built-in List method copy() to copy a list.

Make a copy of a list with the copy() method:

thislist = ["Orlando", "Michael", "Pilar"]
mylist = thislist.copy()
print(mylist)
Use the list() method
Another way to make a copy is to use the built-in method list().

Make a copy of a list with the list() method:

thislist = ["Orlando", "Michael", "Pilar"]
mylist = list(thislist)
print(mylist)

Use the slice Operator
You can also make a copy of a list by using the : (slice) operator.

Make a copy of a list with the : operator:

thislist = ["Orlando", "Michael", "Pilar"]
mylist = thislist[:]
print(mylist)
Exercise
What is a correct syntax for making a copy of a list?

list2 = list1
list2 = list1.copy()
list2.copy(list1)

https://www.w3schools.com/python/python_lists_copy.asp

Join Lists
----------
Join Two Lists
--------------
There are several ways to join, or concatenate, two or more lists in Python.

One of the easiest ways are by using the + operator.

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]

list3 = list1 + list2
print(list3)

Another way to join two lists is by appending all the items from list2 into list1, one by one:

Append list2 into list1:

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3
]
for x in list2:
list1.append(x
)
print(list1)

Or you can use the extend() method, where the purpose is to add elements from one list to another list:

Use the extend() method to add list2 at the end of list1:

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]

list1.extend(list2)
print(list1)

What is a correct syntax for joining list1 and list2 into list3?

list3 = join(list1, list2)
list3 = list1 + list2
list3 = [list1, list2]

List Methods
------------
Python has a set of built-in methods that you can use on lists.

Method Description

append() #Adds an element at the end of the list

clear() #Removes all the elements from the list

copy() #Returns a copy of the list

count() #Returns the number of elements with the specified value

extend() #Add the elements of a list (or any iterable), #to the end of the current list

index() #Returns the index of the first element with the specified value

insert() #Adds an element at the specified position

pop() #Removes the element at the specified position

remove() #Removes the item with the specified value

reverse() #Reverses the order of the list

sort() #Sorts the list

tuple data types examples
-------------------------

tuple Represents ordered, immutable sequences of items.

range data types examples
-------------------------

range Represents a sequence of numbers, often used in loops.

Mapping data types examples
---------------------------
dict Represents a dictionary (key-value pairs).

Set data types examples
-----------------------
set Represents an unordered collection of unique items.
frozenset Represents an immutable set.

Binary data types examples
--------------------------
bytes: Represents immutable sequences of bytes.
bytearray: Represents mutable sequences of bytes.
memoryview: Provides a memory view of an object.

None data types examples
------------------------
NoneType: Represents the absence of a value, the only value being None