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Monday, December 30, 2024

Python tuples Accessing Tuple Items by Index

Definition of Tuples
- Tuples are used to store multiple items in a single variable.
- One of the four built-in data types in Python to store collections of data: List, Tuple, Set, and Dictionary.
- Tuples are ordered and unchangeable collections.
- Written with round brackets ( ).

Tuple Example

mytuple = ("apple", "banana", "cherry")
print(mytuple)

Tuple Properties
- Ordered: Items have a defined order that does not change.
- Unchangeable: Items cannot be modified, added, or removed once the tuple is created.
- Allows Duplicates: Tuples can contain duplicate values.
Tuple Indexing
- Tuple items are indexed starting from [0] for the first item, [1] for the second, and so on.

Example of Duplicate Values

thistuple = ("apple", "banana", "cherry", "apple", "cherry")
print(thistuple)

Tuple Length
- Use the len() function to determine the number of items in a tuple.
  Example:
```
thistuple = ("apple", "banana", "cherry")
print(len(thistuple))
```

Tuple With One Item

To create a single-item tuple, include a trailing comma:

thistuple = ("apple",)  # Tuple
print(type(thistuple))
thistuple = ("apple")  # Not a tuple
print(type(thistuple))

Tuple Items - Data Types
- Items in a tuple can be of any data type. Examples:
  - Strings: tuple1 = ("apple", "banana", "cherry")
  - Integers: tuple2 = (1, 5, 7, 9, 3)
  - Booleans: tuple3 = (True, False, False)
- A tuple can also mix different data types:
```
tuple1 = ("abc", 34, True, 40, "male")
```
Tuple Data Type
- Tuples are objects of the data type <class 'tuple'>. Example:
```
mytuple = ("apple", "banana", "cherry")
print(type(mytuple))
```

The tuple() Constructor

Tuples can also be created using the tuple() constructor. Example:

thistuple = tuple(("apple", "banana", "cherry"))  # Double round brackets
print(thistuple)

Python Collections Overview
- List: Ordered, changeable, allows duplicates.
- Tuple: Ordered, unchangeable, allows duplicates.
- Set: Unordered, unindexed, no duplicates, items are unchangeable (but can be added/removed).
- Dictionary: Ordered (from Python 3.7 onwards), changeable, no duplicate keys.
Choosing a Collection Type
- Understanding the properties of collection types is essential for efficiency, meaning retention, and security.
Exercise Example

Identify the tuple:

thistuple = ('apple', 'banana', 'cherry')  # Tuple
thistuple = ['apple', 'banana', 'cherry']  # List
thistuple = {'apple', 'banana', 'cherry'}  # Set

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Accessing Tuple Items by Index
- Use square brackets [ ] to access tuple items by their index.
- Example:
```
thistuple = ("apple", "banana", "cherry")
print(thistuple[1])  # Output: banana
```
- Note: The first item has index 0.
Negative Indexing
- Negative indexing starts from the end of the tuple.
- -1 refers to the last item, -2 refers to the second last item, and so on.
- Example:
```
thistuple = ("apple", "banana", "cherry")
print(thistuple[-1])  # Output: cherry
```
Range of Indexes
- Specify a range of indexes to retrieve multiple items.
- The result is a new tuple with the specified items.
- Example:
```
thistuple = ("apple", "banana", "cherry", "orange", "kiwi", "melon", "mango")
print(thistuple[2:5])  # Output: ('cherry', 'orange', 'kiwi')
```
- Note: The range includes the start index but excludes the end index.

Leaving Out Start Value

Leaving out the start index begins the range from the first item.

Example:

thistuple = ("apple", "banana", "cherry", "orange", "kiwi", "melon", "mango")
print(thistuple[:4])  # Output: ('apple', 'banana', 'cherry', 'orange')

Leaving Out End Value

Leaving out the end index continues the range to the last item.

Example:

thistuple = ("apple", "banana", "cherry", "orange", "kiwi", "melon", "mango")
print(thistuple[2:])  # Output: ('cherry', 'orange', 'kiwi', 'melon', 'mango')

Range of Negative Indexes

Use negative indexes to specify a range starting from the end.

Example:

thistuple = ("apple", "banana", "cherry", "orange", "kiwi", "melon", "mango")
print(thistuple[-4:-1])  # Output: ('orange', 'kiwi', 'melon')

Check if an Item Exists

Use the in keyword to check if a specific item exists in a tuple.

Example:

thistuple = ("apple", "banana", "cherry")
if "apple" in thistuple:
    print("Yes, 'apple' is in the fruits tuple")

Exercise Question
- What is the index number of the first item?
  Answer: 0.

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Here are all the key points summarized from the provided text about updating tuples in Python:

1. Tuples Are Unchangeable (Immutable)

Tuples are immutable, meaning you cannot change, add, or remove items once created.
However, workarounds exist.

2. Change Tuple Values

Tuples themselves cannot be directly modified, but you can:
1. Convert the tuple into a list.
2. Modify the list.
3. Convert the list back into a tuple.

Example:

x = ("apple", "banana", "cherry")
y = list(x)
y[1] = "kiwi"
x = tuple(y)
print(x)  # Output: ('apple', 'kiwi', 'cherry')

3. Add Items to a Tuple

Tuples do not have an append() method, but you can add items using two approaches:

(1) Convert into a List:
- Convert the tuple into a list, add the new item(s), and convert it back into a tuple.
  Example:
```
thistuple = ("apple", "banana", "cherry")
y = list(thistuple)
y.append("orange")
thistuple = tuple(y)
print(thistuple)  # Output: ('apple', 'banana', 'cherry', 'orange')
```
(2) Add Tuple to Tuple:
- Create a new tuple with the additional item(s) and concatenate it to the existing tuple.
  Example:
```
thistuple = ("apple", "banana", "cherry")
y = ("orange",)
thistuple += y
print(thistuple)  # Output: ('apple', 'banana', 'cherry', 'orange')
```
Note: When creating a tuple with one item, always include a comma (,) after the item to identify it as a tuple.

4. Remove Items from a Tuple

Direct removal is not possible because tuples are immutable.
Workaround: Convert the tuple into a list, remove the item(s), and convert it back into a tuple.

Example:

thistuple = ("apple", "banana", "cherry")
y = list(thistuple)
y.remove("apple")
thistuple = tuple(y)
print(thistuple)  # Output: ('banana', 'cherry')

Delete the Entire Tuple:

Use the del keyword to delete the entire tuple.
Example:

thistuple = ("apple", "banana", "cherry")
del thistuple
# print(thistuple) will raise an error because the tuple no longer exists

5. Exercise Question

You cannot change the items of a tuple, but there are workarounds. Which of the following suggestions will work?

Correct Answer:
- Convert tuple into a list, change item, convert back into a tuple.
Incorrect Answers:
- Convert tuple into a set, change item, convert back into a tuple.
- Convert tuple into a dictionary, change item, convert back into a tuple.

----

Here are all the key points summarized from the provided text about unpacking tuples in Python:

1. Packing a Tuple

Packing refers to assigning multiple values to a tuple.
Example:

fruits = ("apple", "banana", "cherry")

2. Unpacking a Tuple

Unpacking is extracting the values from a tuple into individual variables.
The number of variables must match the number of items in the tuple, unless an asterisk is used.
Example:

fruits = ("apple", "banana", "cherry")
(green, yellow, red) = fruits

print(green)   # Output: apple
print(yellow)  # Output: banana
print(red)     # Output: cherry

3. **Using Asterisk (`*`)**

If the number of variables is less than the number of tuple items, an asterisk (*) can be used to collect the remaining values into a list.

Example 1: Assign the remaining values to the last variable:

fruits = ("apple", "banana", "cherry", "strawberry", "raspberry")
(green, yellow, *red) = fruits

print(green)   # Output: apple
print(yellow)  # Output: banana
print(red)     # Output: ['cherry', 'strawberry', 'raspberry']

Example 2: Assign the remaining values to a middle variable:

The asterisk can be added to a variable that is not the last one. Python will adjust values to fit the remaining variables.

fruits = ("apple", "mango", "papaya", "pineapple", "cherry")
(green, *tropic, red) = fruits

print(green)   # Output: apple
print(tropic)  # Output: ['mango', 'papaya', 'pineapple']
print(red)     # Output: cherry

4. Exercise Question

Consider the following code:

fruits = ('apple', 'banana', 'cherry')
(x, y, z) = fruits
print(y)

What will be the value of y?

Correct Answer: banana

--------------------------

Here are all the key points about looping through tuples in Python:

1. Loop Through a Tuple Using a `for` Loop

You can directly iterate through tuple items using a for loop. Example:

thistuple = ("apple", "banana", "cherry")
for x in thistuple:
    print(x)

2. Loop Through a Tuple Using Index Numbers

You can iterate through a tuple by referring to its index numbers.
Use the range() and len() functions to create an iterable sequence of index numbers. Example:

thistuple = ("apple", "banana", "cherry")
for i in range(len(thistuple)):
    print(thistuple[i])

3. Loop Through a Tuple Using a `while` Loop

A while loop can also be used to iterate through a tuple.
Use the len() function to determine the length of the tuple.
Start at index 0 and increase the index by 1 after each iteration. Example:

thistuple = ("apple", "banana", "cherry")
i = 0
while i < len(thistuple):
    print(thistuple[i])
    i += 1

4. Exercise Question

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

Options:

for x in ('apple', 'banana', 'cherry'):
    print(x)

for x in ('apple', 'banana', 'cherry')
    print(x)

foreach x in ('apple', 'banana', 'cherry')
    print(x)

Correct Answer:
Option 1

for x in ('apple', 'banana', 'cherry'):
    print(x)

---------------------

Here are the key points about joining and multiplying tuples in Python:

1. Join Two Tuples Using the + Operator

You can join two or more tuples by using the + operator.
Example:

tuple1 = ("a", "b", "c")
tuple2 = (1, 2, 3)

tuple3 = tuple1 + tuple2
print(tuple3)  # Output: ('a', 'b', 'c', 1, 2, 3)


2. Multiply Tuples Using the * Operator

You can multiply a tuple to repeat its content a specific number of times using the * operator.
Example:

fruits = ("apple", "banana", "cherry")
mytuple = fruits * 2

print(mytuple)  # Output: ('apple', 'banana', 'cherry', 'apple', 'banana', 'cherry')


3. Exercise Question
What is the correct syntax for joining tuple1 and tuple2 into tuple3?
Options:

tuple3 = join(tuple1, tuple2)
tuple3 = tuple1 + tuple2
tuple3 = [tuple1, tuple2]

Correct Answer:

Option 2
tuple3 = tuple1 + tuple2
----------------------------------
Python - Tuple Methods
Python provides two built-in methods for working with tuples:

1. count() Method

Description: Returns the number of times a specified value occurs in the tuple.
Example:
thistuple = (1, 2, 3, 2, 2, 4)
occurrences = thistuple.count(2)
print(occurrences)  # Output: 3




2. index() Method

Description: Searches the tuple for a specified value and returns the position (index) of its first occurrence.
Example:
thistuple = (1, 2, 3, 4, 5)
position = thistuple.index(3)
print(position)  # Output: 2




These methods can be applied directly to any tuple to analyze or retrieve specific data.

Friday, December 27, 2024

Python Lists Creating Properties Items Length Data Types Constructor Collections syntax

Python Lists
- Lists are used to store multiple items in a single variable.
- One of the four built-in data types in Python used to store collections of data (the others are Tuple, Set, and Dictionary).
Creating Lists
- Lists are created using square brackets ([]).
- Example:
```
thislist = ["apple", "banana", "cherry"]
print(thislist)
```
List Properties
- Ordered: Items have a defined order, which doesn’t change unless explicitly altered.
- Changeable: You can add, remove, and modify items after creation.
- Allow Duplicates: Lists can have items with duplicate values.
List Items
- Items are indexed: The first item has index [0], the second [1], and so on.
- Example of duplicate values:
```
thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)
```
List Length
- Use len() to determine the number of items in a list.
- Example:
```
thislist = ["apple", "banana", "cherry"]
print(len(thislist))
```
List Items - Data Types
- List items can be of any data type (string, integer, boolean, etc.).
- A list can even contain mixed data types.
- Examples:
```
list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]
list4 = ["abc", 34, True, 40, "male"]
```
Type of a List
- From Python’s perspective, lists are objects of the data type 'list'.
- Example:
```
mylist = ["apple", "banana", "cherry"]
print(type(mylist))
```

The list() Constructor

You can create a list using the list() constructor.

Example:

thislist = list(("apple", "banana", "cherry"))  # note the double round brackets
print(thislist)

Python Collections (Arrays)
- List: Ordered and changeable. Allows duplicates.
- Tuple: Ordered and unchangeable. Allows duplicates.
- Set: Unordered, unchangeable*, unindexed. No duplicates.
- Dictionary: Ordered** and changeable. No duplicates.
- Notes:
  - Set items are unchangeable, but you can add/remove items.
  - Dictionaries are ordered as of Python 3.7.
Choosing a Collection Type
- Understanding properties of different types is crucial for efficiency, security, and meaning retention.
Exercise Example

What will be the result of the syntax:

mylist = ['apple', 'banana', 'cherry']
print(mylist[1])

Answer: banana.

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Python List Items:

Access Items by Index

Indexed access: Use index numbers to access list items. Index starts at 0.

thislist = ["apple", "banana", "cherry"]
print(thislist[1])  # Output: "banana"

Note: The first item has index 0.

Negative Indexing

Access from the end: Negative indexing starts at -1 for the last item.

thislist = ["apple", "banana", "cherry"]
print(thislist[-1])  # Output: "cherry"

Examples:
- -1 = Last item
- -2 = Second-last item

Range of Indexes

Slice a range: Specify start and end indexes for a subset.

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(thislist[2:5])  # Output: ['cherry', 'orange', 'kiwi']

Important Notes:
- Start index is included, end index is not included.
- Start defaults to 0 if omitted.
- End defaults to last item if omitted.

Examples:

# From the beginning to "kiwi" (not included)
print(thislist[:4])  # Output: ['apple', 'banana', 'cherry', 'orange']

# From "cherry" to the end
print(thislist[2:])  # Output: ['cherry', 'orange', 'kiwi', 'melon', 'mango']

Range of Negative Indexes

Use negative indexes to slice from the end.

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(thislist[-4:-1])  # Output: ['orange', 'kiwi', 'melon']

Example: Start at -4 ("orange") and end before -1 ("mango").

Check if Item Exists

Use the in keyword to check if an item is in a list.

thislist = ["apple", "banana", "cherry"]
if "apple" in thislist:
    print("Yes, 'apple' is in the fruits list")

Exercise

What will be the result of the following syntax?

mylist = ['apple', 'banana', 'cherry']
print(mylist[-1])

Answer: cherry.

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Changing Python List Items

1. Change Item Value

To change a specific item, use its index:

thislist = ["apple", "banana", "cherry"]
thislist[1] = "blackcurrant"
print(thislist)  # Output: ['apple', 'blackcurrant', 'cherry']

2. Change a Range of Item Values

Replace a range with a new list:

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "mango"]
thislist[1:3] = ["blackcurrant", "watermelon"]
print(thislist)  # Output: ['apple', 'blackcurrant', 'watermelon', 'orange', 'kiwi', 'mango']

3. Insert More Items Than Replaced

If the new list has more items than the replaced range, the extra items are inserted, shifting the remaining elements:

thislist = ["apple", "banana", "cherry"]
thislist[1:2] = ["blackcurrant", "watermelon"]
print(thislist)  # Output: ['apple', 'blackcurrant', 'watermelon', 'cherry']

4. Insert Fewer Items Than Replaced

If the new list has fewer items than the replaced range, the remaining elements shift accordingly:

thislist = ["apple", "banana", "cherry"]
thislist[1:3] = ["watermelon"]
print(thislist)  # Output: ['apple', 'watermelon']

5. Insert Items Without Replacing

Use the insert() method to add an item at a specific index without replacing existing items:

thislist = ["apple", "banana", "cherry"]
thislist.insert(2, "watermelon")
print(thislist)  # Output: ['apple', 'banana', 'watermelon', 'cherry']

Exercise

What will be the result of the following syntax?

mylist = ['apple', 'banana', 'cherry']
mylist[0] = 'kiwi'
print(mylist[1])

Answer: banana.

Explanation:

mylist[0] = 'kiwi' replaces "apple" with "kiwi."
The list becomes ['kiwi', 'banana', 'cherry'].
Printing mylist[1] outputs the second item, which is "banana".

Key Points on Adding Items to Python Lists

1. Append Items

Use the append() method to add an item to the end of the list:

thislist = ["apple", "banana", "cherry"]
thislist.append("orange")
print(thislist)  # Output: ['apple', 'banana', 'cherry', 'orange']

2. Insert Items

Use the insert() method to add an item at a specified index:

thislist = ["apple", "banana", "cherry"]
thislist.insert(1, "orange")
print(thislist)  # Output: ['apple', 'orange', 'banana', 'cherry']

3. Extend List

Use the extend() method to append elements from another list:

thislist = ["apple", "banana", "cherry"]
tropical = ["mango", "pineapple", "papaya"]
thislist.extend(tropical)
print(thislist)  # Output: ['apple', 'banana', 'cherry', 'mango', 'pineapple', 'papaya']

Note: The elements of the second list are added to the end of the current list.

4. Add Any Iterable

The extend() method can also append elements from any iterable object (e.g., tuples, sets, or dictionaries):

thislist = ["apple", "banana", "cherry"]
thistuple = ("kiwi", "orange")
thislist.extend(thistuple)
print(thislist)  # Output: ['apple', 'banana', 'cherry', 'kiwi', 'orange']

Exercise

What will be the result of the following syntax?

mylist = ['apple', 'banana', 'cherry']
mylist.insert(0, 'orange')
print(mylist[1])

Answer: apple.

Explanation:

mylist.insert(0, 'orange') inserts "orange" at index 0.
The updated list becomes ['orange', 'apple', 'banana', 'cherry'].
Printing mylist[1] outputs the second item, which is "apple".

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Key Points on Removing Items from Python Lists

1. Remove a Specified Item

Use the remove() method to remove the first occurrence of the specified value:

thislist = ["apple", "banana", "cherry"]
thislist.remove("banana")
print(thislist)  # Output: ['apple', 'cherry']

If there are duplicate items, remove() will only remove the first occurrence:

thislist = ["apple", "banana", "cherry", "banana", "kiwi"]
thislist.remove("banana")
print(thislist)  # Output: ['apple', 'cherry', 'banana', 'kiwi']

2. Remove an Item by Index

Use the pop() method to remove the item at a specific index:

thislist = ["apple", "banana", "cherry"]
thislist.pop(1)
print(thislist)  # Output: ['apple', 'cherry']

If no index is specified, pop() will remove the last item:

thislist = ["apple", "banana", "cherry"]
thislist.pop()
print(thislist)  # Output: ['apple', 'banana']

3. Remove an Item Using `del`

Use the del keyword to remove an item at a specific index:

thislist = ["apple", "banana", "cherry"]
del thislist[0]
print(thislist)  # Output: ['banana', 'cherry']

Use del to delete the entire list:

thislist = ["apple", "banana", "cherry"]
del thislist
# List no longer exists

4. Clear the Entire List

Use the clear() method to empty the list while keeping the list object:

thislist = ["apple", "banana", "cherry"]
thislist.clear()
print(thislist)  # Output: []

Exercise

What is a list method for removing list items?

Options:
- pop() ✅
- push() ❌
- delete() ❌

Answer: pop().

Explanation:

pop() is a built-in method for removing items from a list by index.

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Looping Through Python Lists

1. Loop Through a List Using `for` Loop

You can directly loop through the items in a list:

thislist = ["apple", "banana", "cherry"]
for x in thislist:
    print(x)

Output:

apple
banana
cherry

2. Loop Through the List Using Index Numbers

Use range() and len() to loop through items by their index:
```
thislist = ["apple", "banana", "cherry"]
for i in range(len(thislist)):
    print(thislist[i])
```
Output:
```
apple
banana
cherry
```
- Here, the range [0, 1, 2] is created for the list indices.

3. Loop Through a List Using a `while` Loop

Use the while loop with the index and the length of the list:

thislist = ["apple", "banana", "cherry"]
i = 0
while i < len(thislist):
    print(thislist[i])
    i += 1

Output:

apple
banana
cherry

4. Loop Through a List Using List Comprehension

Use list comprehension for a more concise looping syntax:

thislist = ["apple", "banana", "cherry"]
[print(x) for x in thislist]

Output:

apple
banana
cherry

Exercise

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

Options:

for x in ['apple', 'banana', 'cherry']:
    print(x)
``` ✅

for x in ['apple', 'banana', 'cherry']
    print(x)
``` ❌ (Missing colon `:`)

foreach x in ['apple', 'banana', 'cherry']
    print(x)
``` ❌ (Python does not use `foreach`)

Answer: Option 1.

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Python List Comprehension

1. What is List Comprehension?

Definition: A shorter syntax to create a new list based on values from an existing list.

Example (Traditional Approach):

fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = []

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

print(newlist)

Output:

['apple', 'banana', 'mango']

Example (Using List Comprehension):

fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)

Output:

['apple', 'banana', 'mango']

2. Syntax

newlist = [expression for item in iterable if condition == True]

expression: The item or manipulated version of the item to include in the new list.
iterable: The original list, range, tuple, etc., being iterated.
condition: (Optional) Filters the items to be included in the new list.

3. Condition

Filters the items that evaluate to True.

Example: Exclude "apple":

newlist = [x for x in fruits if x != "apple"]
print(newlist)

Output:

['banana', 'cherry', 'kiwi', 'mango']

Condition is Optional: Without a condition:

newlist = [x for x in fruits]
print(newlist)

Output:

['apple', 'banana', 'cherry', 'kiwi', 'mango']

4. Iterable

Any iterable object can be used, e.g., lists, tuples, sets, etc.

Example: Use range():

newlist = [x for x in range(10)]
print(newlist)

Output:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Example with a condition (Numbers less than 5):

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

Output:

[0, 1, 2, 3, 4]

5. Expression

Manipulate each item in the iteration.

Example: Convert to uppercase:

newlist = [x.upper() for x in fruits]
print(newlist)

Output:

['APPLE', 'BANANA', 'CHERRY', 'KIWI', 'MANGO']

Example: Set all values to "hello":

newlist = ['hello' for x in fruits]
print(newlist)

Output:

['hello', 'hello', 'hello', 'hello', 'hello']

Example: Use condition in the expression (Replace "banana" with "orange"):

newlist = [x if x != "banana" else "orange" for x in fruits]
print(newlist)

Output:

['apple', 'orange', 'cherry', 'kiwi', 'mango']

Exercise

Question:
Given the code:

fruits = ['apple', 'banana', 'cherry']
newlist = [x for x in fruits if x == 'banana']

What will be the value of newlist?

Options:

['apple', 'cherry']
['banana'] ✅
True

Answer: ['banana']

****************

Key Points on Python - Sorting Lists

1. Sort List Alphanumerically (Ascending by Default)

The sort() method sorts lists alphabetically or numerically in ascending order.

Example (Alphabetical Sort):

thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort()
print(thislist)

Output:

['banana', 'kiwi', 'mango', 'orange', 'pineapple']

Example (Numerical Sort):

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

Output:

[23, 50, 65, 82, 100]

2. Sort in Descending Order

Use the keyword argument reverse=True to sort in descending order.

Example (Descending Alphabetical Sort):

thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort(reverse=True)
print(thislist)

Output:

['pineapple', 'orange', 'mango', 'kiwi', 'banana']

Example (Descending Numerical Sort):

thislist = [100, 50, 65, 82, 23]
thislist.sort(reverse=True)
print(thislist)

Output:

[100, 82, 65, 50, 23]

3. Customize the Sort Function

Use the key=function argument to define a custom sort function.

Example (Sort by Distance to 50):

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

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

Output:

[50, 65, 23, 82, 100]

4. Case Sensitivity in Sorting

By default, sort() is case-sensitive, placing uppercase letters before lowercase ones.

Example (Case-Sensitive Sort):

thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort()
print(thislist)

Output:

['Kiwi', 'Orange', 'banana', 'cherry']

5. Case-Insensitive Sorting

Use the key=str.lower argument to perform a case-insensitive sort.

Example:

thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort(key=str.lower)
print(thislist)

Output:

['banana', 'cherry', 'Kiwi', 'Orange']

6. Reverse the Order

The reverse() method reverses the current order of list items, regardless of their values.

Example:

thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.reverse()
print(thislist)

Output:

['cherry', 'Kiwi', 'Orange', 'banana']

Exercise

Question:
What is the correct syntax for sorting a list?

Options:

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

Answer:
mylist.sort()

*****************

Key Points on Python - Copying Lists

1. Problem with Direct Assignment

Direct assignment (list2 = list1) does not create a new list; instead, list2 becomes a reference to list1.
Changes made to list1 will automatically reflect in list2.

2. Using the `copy()` Method

The copy() method creates a shallow copy of the list, independent of the original list.

Example:

thislist = ["apple", "banana", "cherry"]
mylist = thislist.copy()
print(mylist)

Output:

['apple', 'banana', 'cherry']

3. Using the `list()` Method

The list() method can also create a new list from an existing one.

Example:

thislist = ["apple", "banana", "cherry"]
mylist = list(thislist)
print(mylist)

Output:

['apple', 'banana', 'cherry']

4. Using the Slice (`:`) Operator

The slice operator ([:]) creates a copy of the entire list.

Example:

thislist = ["apple", "banana", "cherry"]
mylist = thislist[:]
print(mylist)

Output:

['apple', 'banana', 'cherry']

Exercise

Question:
What is the correct syntax for making a copy of a list?

Options:

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

Answer:
list2 = list1.copy()

Here are all the points related to joining lists in Python:

Using the + Operator: The easiest way to join two lists is by using the + operator.

Example:

list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)

Output:

['a', 'b', 'c', 1, 2, 3]

Using the append() Method: Another way to join two lists is by appending each item from list2 to list1 one by one.

Example:
```
list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
for x in list2:
    list1.append(x)
print(list1)
```
Output:
```
['a', 'b', 'c', 1, 2, 3]
```
Using the extend() Method: You can also use the extend() method, which adds elements from one list to another list.

Example:
```
list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list1.extend(list2)
print(list1)
```
Output:
```
['a', 'b', 'c', 1, 2, 3]
```

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

Options:

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

Correct answer:

list3 = list1 + list2

Here are all the points related to Python list methods:

List Methods in Python:

append()
Adds an element at the end of the list.
Example:
```
list1.append(4)
```
clear()
Removes all the elements from the list.
Example:
```
list1.clear()
```
copy()
Returns a copy of the list.
Example:
```
list2 = list1.copy()
```
count()
Returns the number of elements with the specified value.
Example:
```
list1.count(2)
```
extend()
Adds the elements of a list (or any iterable) to the end of the current list.
Example:
```
list1.extend([4, 5, 6])
```
index()
Returns the index of the first element with the specified value.
Example:
```
list1.index(3)
```
insert()
Adds an element at the specified position.
Example:
```
list1.insert(1, 'a')
```
pop()
Removes the element at the specified position and returns it.
Example:
```
list1.pop(2)
```
remove()
Removes the item with the specified value.
Example:
```
list1.remove(3)
```
reverse()
Reverses the order of the list.
Example:
```
list1.reverse()
```
sort()
Sorts the list.
Example:
```
list1.sort()
```

Thursday, December 26, 2024

What are the 7 Python operators Logical Arithmetic Assignment Bitwise Comparison Membership Online Classes Project Assignments Guide Help

General Overview

Definition: Operators perform operations on variables and values.
Example: print(10 + 5)

Categories of Python Operators

Arithmetic operators
Assignment operators
Comparison operators
Logical operators
Identity operators
Membership operators
Bitwise operators

Details of Each Operator Category

1. Python Arithmetic Operators

Operators and their meanings:
- + (Addition)
- - (Subtraction)
- * (Multiplication)
- / (Division)
- % (Modulus)
- ** (Exponentiation)
- // (Floor division)

2. Python Assignment Operators

Assign values to variables:
- =
- +=
- -=
- *=
- /=
- %=
- //=
- **=
- &=
- |=
- ^=
- >>=
- <<=
- := (Walrus operator)

3. Python Comparison Operators

Compare two values:
- == (Equal)
- != (Not equal)
- > (Greater than)
- < (Less than)
- >= (Greater than or equal to)
- <= (Less than or equal to)

4. Python Logical Operators

Combine conditional statements:
- and
- or
- not

5. Python Identity Operators

Compare object identity (memory location):
- is
- is not

6. Python Membership Operators

Test for presence in a sequence:
- in
- not in

7. Python Bitwise Operators

Compare binary numbers:
- & (AND)
- | (OR)
- ^ (XOR)
- ~ (NOT)
- << (Left shift)
- >> (Right shift)

Python Operator Precedence

Defines the order of evaluation in expressions.
Precedence order (highest to lowest):
1. () Parentheses
2. ** Exponentiation
3. +x, -x, ~x Unary operations
4. *, /, //, % Multiplication, division, floor division, modulus
5. +, - Addition and subtraction
6. <<, >> Bitwise shifts
7. & Bitwise AND
8. ^ Bitwise XOR
9. | Bitwise OR
10. Comparisons, identity, and membership operators
11. not Logical NOT
12. and Logical AND
13. or Logical OR

Examples

Parentheses have the highest precedence:
```
print((6 + 3) - (6 + 3))  
```
Multiplication is evaluated before addition:
```
print(100 + 5 * 3)  
```
Operators with the same precedence are evaluated left to right:
```
print(5 + 4 - 7 + 3)  
```

Exercise

What will be the result of the following syntax?

x = 5  
x += 3  
print(x)

Answer: 8.

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Tuesday, December 24, 2024

Python Strings Definition Quotes Assigning String Slicing Methods Escape Characters Format Concatenation

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Points on Python Strings

Definition of Strings
- Strings in Python are surrounded by either single (') or double (") quotation marks.
  Example:
```
print("Hello")
print('Hello')
```
Quotes Inside Strings
- Quotes inside strings can be used as long as they don't match the outer quotes.
  Example:
```
print("It's alright")
print("He is called 'Johnny'")
print('He is called "Johnny"')
```
Assigning Strings to Variables
- Strings can be assigned to variables using the equal sign (=).
  Example:
```
a = "Hello"
print(a)
```

Multiline Strings

Multiline strings are created using triple quotes (""" or ''').
Example:

a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit."""
print(a)

Or:

a = '''Lorem ipsum dolor sit amet,
consectetur adipiscing elit.'''
print(a)

Strings as Arrays
- Strings are arrays of bytes representing Unicode characters.
- Access elements using square brackets ([]).
  Example:
```
a = "Hello, World!"
print(a[1])  # Outputs 'e'
```
Looping Through a String
- Strings can be iterated using a for loop.
  Example:
```
for x in "banana":
    print(x)
```
String Length
- Use the len() function to get the length of a string.
  Example:
```
a = "Hello, World!"
print(len(a))  # Outputs 13
```

Check String Presence

Use the in keyword to check if a substring is present.
Example:

txt = "The best things in life are free!"
print("free" in txt)  # Outputs True

Use in with an if statement:

if "free" in txt:
    print("Yes, 'free' is present.")

Check String Absence

Use the not in keyword to check if a substring is not present.
Example:

txt = "The best things in life are free!"
print("expensive" not in txt)  # Outputs True

Use not in with an if statement:

if "expensive" not in txt:
    print("No, 'expensive' is NOT present.")

Exercise

Question:
```
x = 'Welcome'
print(x[3])
```
Answer: The output will be:
c (since indexing starts at 0).

Slicing Syntax
- Strings can be sliced using the syntax [start:end].
- The slicing returns characters from the start index up to, but not including, the end index.
  Example:
```
b = "Hello, World!"
print(b[2:5])  # Outputs 'llo'
```
- Note: Indexing starts at 0.
Slice From the Start
- Omitting the start index makes the slice begin from the start of the string.
  Example:
```
b = "Hello, World!"
print(b[:5])  # Outputs 'Hello'
```
Slice To the End
- Omitting the end index makes the slice go until the end of the string.
  Example:
```
b = "Hello, World!"
print(b[2:])  # Outputs 'llo, World!'
```
Negative Indexing
- Negative indices count from the end of the string.
- Example:
```
b = "Hello, World!"
print(b[-5:-2])  # Outputs 'orl'
```
  - Here, -5 corresponds to "o" in "World!" and -2 excludes "d" in "World!".
Exercise

Question:
```
x = 'Welcome'
print(x[3:5])
```
Answer: The output will be:
co (characters from index 3 to 4, as index 5 is not included).

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Points on Python - Modify Strings

Built-in Methods
- Python provides built-in methods to modify strings.
Convert to Upper Case
- The upper() method converts all characters in the string to upper case.
  Example:
```
a = "Hello, World!"
print(a.upper())  # Outputs: "HELLO, WORLD!"
```
Convert to Lower Case
- The lower() method converts all characters in the string to lower case.
  Example:
```
a = "Hello, World!"
print(a.lower())  # Outputs: "hello, world!"
```
Remove Whitespace
- The strip() method removes whitespace from the beginning and the end of the string.
  Example:
```
a = " Hello, World! "
print(a.strip())  # Outputs: "Hello, World!"
```
Replace Substring
- The replace() method replaces a specified substring with another substring.
  Example:
```
a = "Hello, World!"
print(a.replace("H", "J"))  # Outputs: "Jello, World!"
```
Split String
- The split() method splits the string into substrings based on a specified separator and returns them as a list.
  Example:
```
a = "Hello, World!"
print(a.split(","))  # Outputs: ['Hello', ' World!']
```
String Methods Reference
- Python provides many more string methods. Refer to Python's String Methods Reference for a complete list.
Exercise

Question:
What is the correct syntax to print a string in upper case letters?
- 'Welcome'.upper() ✅
- 'Welcome'.toUpper() ❌
- 'Welcome'.toUpperCase() ❌
Correct Answer:
'Welcome'.upper()