Python Tutorial: Loops, Operators, Data Structures, and More
Python Programming Basics
Control Flow: Pass, Continue, and Break
Let’s understand the pass, continue, and break statements in Python:
(i) Pass:
The pass statement is a placeholder. It does nothing but is useful when a statement is syntactically required, but you don’t want any action to be taken.
Example:
if condition:
pass # Do nothing for now
(ii) Continue:
The continue statement is used inside loops. It skips the rest of the current iteration and moves to the next one.
Example:
for i in range(5):
if i == 3:
continue # Skip iteration when i is 3
print(i)
(iii) Break:
The break statement is used to exit a loop prematurely. It’s often used when a certain condition is met, and there’s no need to continue looping.
Example:
for i in range(5):
if i == 3:
break # Exit the loop when i is 3
print(i)
Loops: While and For
While Loop:
A while loop repeatedly executes a block of code as long as a condition is True.
Example:
i = 0
while i < 5:
print(i)
i += 1
For Loop:
A for loop iterates over a sequence (like a list, string, or range) and executes a block of code for each element.
Example:
for i in range(5):
print(i)
Key Differences:
| Feature | While Loop | For Loop |
|---|---|---|
| Condition | Runs as long as a condition is true. | Iterates over a sequence. |
| Use Case | When the number of iterations is unknown. | When the number of iterations is known or for iterating over collections. |
Operators in Python
Python has 7 categories of operators:
- Arithmetic Operators:
+,-,*,/,%,**,//(Perform mathematical operations) - Comparison Operators:
==,!=,>,<,>=,<=(Compare values) - Assignment Operators:
=,+=,-=,*=, etc. (Assign values to variables) - Logical Operators:
and,or,not(Combine or negate conditions) - Bitwise Operators:
&,|,^,~,<<,>>(Operate on bits) - Membership Operators:
in,not in(Check for membership in a sequence) - Identity Operators:
is,is not(Check if objects are the same)
(Examples for each operator category are provided in the original HTML, which can be included here if needed)
Python Execution Modes
Interactive Mode:
- Code is executed line by line.
- Great for quick testing and experimentation.
Script Mode:
- Code is written in a file and executed as a whole.
- Used for writing complete programs.
More Python Concepts
1. Membership Operators:
Check if a value is present in a sequence (e.g., list, string).
Example:
my_list = [1, 2, 3]
print(2 in my_list) # True
2. Identity Operators:
Check if two variables refer to the same object in memory.
Example:
a = [1, 2]
b = a
print(a is b) # True
3. Escape Sequences:
Represent special characters in strings (e.g., newline, tab).
Example:
print("Hello\nWorld") # Prints on two lines
4. Slicing:
Extract a portion of a sequence (e.g., list, string).
Example:
my_string = "Python"
print(my_string[1:4]) # yth
String Functions: lstrip(), swapcase(), isspace()
1. lstrip():
Removes leading whitespace from a string.
Example:
text = " Hello"
print(text.lstrip()) # "Hello"
2. swapcase():
Swaps the case of letters in a string.
Example:
text = "Hello"
print(text.swapcase()) # "hELLO"
3. isspace():
Checks if a string contains only whitespace.
Example:
text = " "
print(text.isspace()) # True
Dictionaries in Python
A dictionary stores data in key-value pairs.
Creating Dictionaries:
- Using curly braces:
my_dict = {"name": "Alice", "age": 30} - Using
dict():my_dict = dict(name="Alice", age=30)
List Methods: reverse(), insert(), remove(), pop()
1. reverse():
Reverses the list in place.
Example:
my_list = [1, 2, 3]
my_list.reverse()
print(my_list) # [3, 2, 1]
2. insert():
Inserts an element at a specific index.
Example:
my_list = [1, 2, 3]
my_list.insert(1, 4)
print(my_list) # [1, 4, 2, 3]
3. remove():
Removes the first occurrence of an element.
Example:
my_list = [1, 2, 3, 2]
my_list.remove(2)
print(my_list) # [1, 3, 2]
4. pop():
Removes and returns the element at a specific index (or the last element if no index is specified).
Example:
my_list = [1, 2, 3]
removed_element = my_list.pop(1)
print(my_list) # [1, 3]
print(removed_element) # 2
Mutable vs. Immutable Objects
Mutable:
- Can be changed after creation (e.g., lists, dictionaries).
Immutable:
- Cannot be changed after creation (e.g., strings, tuples).
Tuples in Python
Tuples are ordered, immutable collections.
Defining and Accessing Tuples:
Example:
my_tuple = (1, 2, "apple")
print(my_tuple[0]) # 1
Dictionary Methods: keys(), values(), items(), clear(), copy(), update(), get()
1. keys():
Returns a view of the dictionary’s keys.
2. values():
Returns a view of the dictionary’s values.
3. items():
Returns a view of the dictionary’s key-value pairs.
4. clear():
Removes all items from the dictionary.
5. copy():
Creates a shallow copy of the dictionary.
6. update():
Updates the dictionary with key-value pairs from another dictionary or iterable.
7. get():
Returns the value for a key (or a default value if the key is not found).
(Examples for each dictionary method can be included from the original HTML if needed)
List Slicing
Example:
alphabet = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']
# First 3 letters
print(alphabet[:3]) # ['A', 'B', 'C']
# Middle 3 letters
print(alphabet[3:6]) # ['D', 'E', 'F']
# From index 5 to the end
print(alphabet[5:]) # ['F', 'G', 'H', 'I', 'J']
Removing Duplicates from a List
Example:
numbers = [1, 2, 2, 3, 4, 4, 5]
unique_numbers = list(set(numbers))
print(unique_numbers) # [1, 2, 3, 4, 5]
Printing Odd/Even Numbers from a List
Example:
numbers = [1, 2, 3, 4, 5, 6]
even_numbers = []
odd_numbers = []
for num in numbers:
if num % 2 == 0:
even_numbers.append(num)
else:
odd_numbers.append(num)
print("Even numbers:", even_numbers) # [2, 4, 6]
print("Odd numbers:", odd_numbers) # [1, 3, 5]