Update python.md

python.md

@@ -3,118 +3,141 @@ title: Python
 category: Python
 ---
 
-### Tuples (immutable)
+### Tuples (Immutable)
 
 ```py
-tuple = ()
+t = ()  # Empty tuple
+t = (1, 2, 3)  # Tuple with elements
+t = (1,)  # Single-element tuple (comma is required)
+
+# Accessing elements
+t[0]  # First element
+t[-1]  # Last element
+
+# Methods
+len(t)  # Get the length
 ```
 
-### Lists (mutable)
+### Lists (Mutable)
 
 ```py
-list = []
-list[i:j]  # returns list subset
-list[-1]   # returns last element
-list[:-1]  # returns all but the last element
-*list      # expands all elements in place
+lst = []  # Empty list
+lst = [1, 2, 3]  # List with elements
+
+# Accessing and slicing
+lst[i:j]  # Sublist from index i to j-1
+lst[-1]  # Last element
+lst[:-1]  # All but the last element
+
+# Modifications
+lst[i] = value  # Set an element
+lst.append(value)  # Add to the end
+lst.insert(i, value)  # Insert at position i
+lst.extend([1,2,3])  # Extends list with another list
+lst.pop()  # Remove and return element. Can also accept an index.
+lst.remove(value)  # Remove first occurrence of value
+del lst[i:j]  # Delete slice between i and j-1
+list1 + list2  # combine two list
+
+# Useful methods
+lst.sort()  # In-place sort
+sorted(lst)  # Sorted copy
+lst.reverse()  # In-place reverse
+list(reversed(lst)) # Reversed copy
+list.count(value)  # Counts number of elements with the specified value
+",".join(lst)  # Join elements into a string if all elements are strings
+",".join(map(str, lst))  # Join elements into a string
+```
 
-list[i] = val
-list[i:j] = otherlist  # replace ith to jth-1 elements with otherlist
-del list[i:j]
+### Dictionaries (Key-Value Pairs)
 
-list.append(item)
-list.extend(another_list)
-list.insert(index, item)
-list.pop()        # returns and removes last element from the list
-list.pop(i)       # returns and removes i-th element from the list
-list.remove(i)    # removes the first item from the list whose value is i
-list1 + list2     # combine two list    
-set(list)         # remove duplicate elements from a list
+```py
+d = {}  # Empty dict
+d = {"a": 1, "b": 2}  # Initialize with values
 
-list.reverse()    # reverses the elements of the list in-place
-list.count(item)
-sum(list)
+# Accessing and modifying
+d["key"]  # Access value
+d.get("key", "default")  # Safe access with default
+d["key"] = value  # Add or update
+d.setdefault("key", "default")   # If no key, insert with the specified value
+del d["key"]  # Delete key-value pair
+"key" in d  # Checks if key in dict
 
-zip(list1, list2)  # returns list of tuples with n-th element of both list1 and list2
-list.sort()        # sorts in-place, returns None
-sorted(list)       # returns sorted copy of list
-",".join(list)     # returns a string with list elements separated by comma
+# Iteration
+for key, value in d.items():  # Iterate over key-value pairs
+    print(key, value)
 
-```
+# Useful methods
+list(d.keys() ) # List of keys
+list(d.values())  # List of values
+list(d.items())  # List of key-value pairs
 
-### Dict
 
-```py
-dict = {}
-dict = {'a': 1, 'b': 2}
-dict['c'] = 3
-del dict['a']    # Remove key-value pair with key 'c'
-dict.keys()
-dict.values()
-"key" in dict    # let's say this returns False, then...
-dict["key"]      # if "key" not in dict raises KeyError
-dict.get("key")  # if "key" not in dict returns None
-dict.get("key", "optional return value if no key")
-dict.setdefault("key", 1)
-**dict           # expands all k/v pairs in place
+# Error cases:
+d["key"]  # if "key" not in dict raises KeyError
+d.get("key")  # if "key" not in dict returns None
+
+** dict  # expands all k/v pairs in place
 ```
 
 ### Set
 
 ```py
-set = set()
-set = {1, 2, 3}
-set.add(4)
-set.remove(2) 
+s = set()  # Empty set
+s = {1, 2, 3}  # Set with values
+s = set([1, 2, 3, 3])  # Convert List into Set
+
+# Modifications
+s.add(4)  # Add element
+s.remove(2)  # Remove element
+
+# Set operations
+s1 | s2  # Union
+s1 & s2  # Intersection
+s1 - s2  # Difference
+s1 ^ s2  # Symmetric difference
 ```
 
 ### Iteration
 
 ```py
-for item in ["a", "b", "c"]:
-for i in range(4):        # 0 to 3
-for i in range(4, 8):     # 4 to 7
-for i in range(1, 9, 2):  # 1, 3, 5, 7
-for key, val in dict.items():
-for index, item in enumerate(list):
+for i in range(4):  # 0 to 3
+for i in range(4, 8):  # 4 to 7
+for i in range(1, 9, 2):  # 1, 3, 5, 7 from 1 to 8 step by 2
+for item in lst:
+for key, value in dict.items(): 
+for index, value in enumerate(lst):
 ```
 
-### [String](https://docs.python.org/2/library/stdtypes.html#string-methods)
+### [String Manipulation](https://docs.python.org/2/library/stdtypes.html#string-methods)
 
 ```py
-str[0:4]
-len(str)
-
-string.replace("-", " ")
-",".join(list)
-"hi {0}".format('j')
-f"hi {name}" # same as "hi {}".format('name')
-str.find(",")
-str.index(",")   # same, but raises IndexError
-str.count(",")
-str.split(",")
-
-str.lower()
-str.upper()
-str.title()
-
-str.lstrip()
-str.rstrip()
-str.strip()
-
-str.islower()
-
-/* escape characters */
->>> 'doesn\'t'  # use \' to escape the single quote...
-    "doesn't"
->>> "doesn't"  # ...or use double quotes instead
-    "doesn't"
->>> '"Yes," they said.'
-    '"Yes," they said.'
->>> "\"Yes,\" they said."
-    '"Yes," they said.'
->>> '"Isn\'t," they said.'
-    '"Isn\'t," they said.'
+s = "hello world"
+
+# Basic methods
+s.upper()  # HELLO WORLD
+s.lower()  # hello world
+s.strip()  # Remove leading/trailing spaces
+s.lstrip() or s.rstrip()
+lst = s.split(" ")  # Split by space into list
+s.replace("world", "Python")  # Replace substring
+",".join(["a", "b", "c"])  # Join elements with a separator
+
+str.count(value)  # Count # of values
+str.find(value)  # Returns first index of value in str, -1 otherwise
+str.index(value)  # same, but raises IndexError
+
+str.isalpha()  # True if all the chars are alphabet letters(a-z).
+str.isdigit()  # True if digit(s)
+
+# Formatting
+f"Hello, {name}!"  # f-string
+"Hello, {}!".format(name)  # Same as f-string
+"{:.2f}".format(3.14159)  # Format float to 2 decimals
+
+# Escape Characters
+print('doesn\'t')  # Use \' to escape the single quote
+print("doesn't")  # Or use double quotes instead
 ```
 
 ### Casting
@@ -130,18 +153,76 @@ str(float)
 ### Comprehensions
 
 ```py
-[fn(i) for i in list]            # .map
-map(fn, list)                    # .map, returns iterator
+# List comprehension
+squared = [x ** 2 for x in range(10)]
+
+# Dictionary comprehension
+squared_dict = {x: x ** 2 for x in range(10)}
+
+# Set comprehension
+unique = {x for x in lst if x > 0}
+
+# Filter and map
+filtered = [x for x in lst if x > 0]
+transformed = list(map(str, lst))
+
+[fn(i) for i in list]  # .map
+map(fn, list)  # .map, returns iterator
+
+filter(fn, list)  # .filter, returns iterator
+[fn(i) for i in list if i > 0]  # .filter.map
+```
+
+### Queues (FIFO)
+```py
+from collections import deque
+
+queue = deque()  # Initialize
+queue.append(1)  # Enqueue
+print(queue.popleft())  # Dequeue (FIFO)
+print(queue.pop())  # LIFO: Remove and return last element
+```
+
+#### Using queue.Queue (Thread-Safe):
+```py
+from queue import Queue
 
-filter(fn, list)                 # .filter, returns iterator
-[fn(i) for i in list if i > 0]   # .filter.map
+q = Queue()
+q.put(1)  # Enqueue
+print(q.get())  # Dequeue (FIFO)
+print(q.qsize())  # Current size
+print(q.empty())  # Check if empty
 ```
 
-### Regex
+### Priority Queues
+```py
+from queue import PriorityQueue
+
+pq = PriorityQueue()
+pq.put((2, "B"))  # Insert with priority 2
+pq.put((1, "A"))  # Insert with priority 1
+print(pq.get())  # Dequeue (Lowest priority first): (1, "A")
+```
+
+### Heap
+```py
+import heapq
+
+heapq.heapify(lst)  # Converts a list into a min-heap in-place
+heapq.heappush(heap, item)  # Adds item to the heap while maintaining heap order
+heapq.heappop(heap)  # Removes and returns the smallest element in the heap
+```
+
+
+### Regex (see https://regex101.com)
 
 ```py
 import re
 
+pattern = r"^\d+$"  # Matches integers
+if re.match(pattern, "123"):
+    print("It's a number!")
+
 re.match(r'^[aeiou]', str)
 re.sub(r'^[aeiou]', '?', str)
 re.sub(r'(xyz)', r'\1', str)
@@ -151,38 +232,67 @@ expr.match(...)
 expr.sub(...)
 ```
 
+## Tips & Tricks
+
+## Sorting
+
+```py
+sorted(lst)  # Ascending order
+sorted(lst, reverse=True)  # Descending order
+lst.sort(key=lambda x: x[1])  # Custom sort by second element
+```
+
+## Useful Built-ins
+```py
+sum(lst)  # Sum of elements
+max(lst)  # Maximum element
+min(lst)  # Minimum element
+zip(lst1, lst2)  # Pair elements
+all(lst)  # True if all elements are true
+any(lst)  # True if any element is true
+```
+
 ## File manipulation
-    
+
 ### Reading
 
 ```py
-file = open("hello.txt", "r") # open in read mode 'r'
-file.close() 
+file = open("hello.txt", "r")  # open in read mode 'r'
+content = f.read()  # Read entire file
+lines = f.readlines()  # Read all lines as a list
+file.close()
+
+# Alternative
+with open("file.txt", "r") as f:
+    content = f.read()  # Read entire file
+    lines = f.readlines()  # Read all lines as a list
 ```
 
 ```py
-print(file.read())  # read the entire file and set the cursor at the end of file
-print file.readline() # Reading one line
-file.seek(0, 0) # place the cursor at the beginning of the file
+file.read()  # read the entire file and set the cursor at the end of file
+file.readline()  # Reading one line
+file.seek(0, 0)  # place the cursor at the beginning of the file
 ```
 
 ### Writing (overwrite)
 
 ```py
-file = open("hello.txt", "w") # open in write mode 'w'
-file.write("Hello World") 
-
-text_lines = ["First line", "Second line", "Last line"] 
-file.writelines(text_lines)
-
+file = open("hello.txt", "w")  # open in write mode 'w'
+file.write("Hello World")
+file.writelines(["First line", "Second line", "Last line"])
 file.close()
+
+# Alternative
+with open("file.txt", "w") as f:
+    f.write("Hello, world!")  # Overwrite file
+    f.writelines(["Line1\n", "Line2\n"])  # Write multiple lines
 ```
 
 ### Writing (append)
 
 ```py
-file = open("Hello.txt", "a") # open in append mode
-file.write("Hello World again")  
+file = open("Hello.txt", "a")  # open in append mode
+file.write("Hello World again")
 file.close()
 ```
 
@@ -191,7 +301,7 @@ file.close()
 ```py
 with open("welcome.txt", "r") as file:
     # 'file' refers directly to "welcome.txt"
-   data = file.read()
+    data = file.read()
 
 # It closes the file automatically at the end of scope, no need for `file.close()`.
 ```