Keywords in Python 🔑

In this section, we will discuss keywords in Python—special identifiers reserved for specific syntactic purposes. Understanding keywords is essential as they form the foundation of Python's syntax and structure.

What are Keywords? 🔍

• Keywords are reserved words in Python that have special meanings and cannot be used as regular identifiers (like variable names or function names).
• Python's keywords consist only of lowercase letters.

Python v2 vs. Python v3 🧩

• Python v2 has 31 keywords.
• Python v3 has 35 keywords.

Example:

# Keywords that cannot be used as identifiers
if = 10  # ❌ Invalid: 'if' is a keyword
def = 20  # ❌ Invalid: 'def' is a keyword

Categories of Keywords 📚

1. Simple Statements and Clauses 📝

• Some keywords begin simple statements or clauses within compound statements.

2. Operators ➗

• Other keywords serve as operators within expressions.

Python v2 Keywords 🔡

In Python v2, the keywords include:

and       continue   except   global    lambda   raise     yield
as        def        exec     if        not      return
assert    del        finally  import    or       try
break     elif       for      in        pass     while
class     else       from     is        print    with

Notable Points in Python v3 🆕

• In Python v3:
  • exec and print are no longer keywords. They were statements in Python v2 but are now functions in Python v3.
  • To use the print function in Python v2, you can start your source file with:

    from __future__ import print_function

  • New keywords in Python v3 include False, None, True, and nonlocal.
    • False, None, and True were built-in constants in Python v2, but they were not technically keywords.
  • Additional Keywords in Python v3 include:
    • async and await: Used for asynchronous programming.

Python v3 Keywords 🔡

In Python v3, the updated list of keywords includes:

and       as         assert    async     await    break
class     continue   def       del       elif     else
except    False      finally   for       from     global
if        import     in        is        lambda   None
nonlocal  not        or        pass      raise    return
True      try        while     with      yield

Common Keywords and Their Uses 📋

Keyword	Description	Code Example
False, True	Data values from the data type Boolean	False == (1 > 2) True == (2 > 1)
and, or, not	Logical operators: - (x and y) → both x and y must be True - (x or y) → either x or y must be True - (not x) → x must be false	x, y = True, False (x or y) == True # True (x and y) == False # True (not y) == True # True
break	Ends loop prematurely	while(True): break # no infinite loop print("hello world")
continue	Finishes current loop iteration	while(True): continue print("43") # dead code
class, def	class defines a new class. def defines a new function or method.	class Beer: def __init__(self): self.content = 1.0 def drink(self): self.content = 0.0 becks = Beer() becks.drink() # empty beer bottle
if, elif, else	Conditional program execution: program starts with if, tries elif, and ends with else.	x = int(input("your val: ")) if x > 3: print("Big") elif x == 3: print("Medium") else: print("Small")
for, while	Looping constructs: for loop iterates over a sequence, while continues as long as the condition is true.	for i in [0, 1, 2]: print(i) j = 0 while j < 3: print(j) j += 1
in	Checks whether an element is in a sequence	42 in [2, 39, 42] # True
is	Checks whether two references point to the same object	y = x = 3 x is y # True [3] is [3] # False
None	Represents a null value or absence of value	def f(): x = 2 f() is None # True
lambda	Defines a small anonymous function	(lambda x: x + 3)(3) # returns 6
return	Ends the execution of a function and optionally returns a value	def incrementor(x): return x + 1 incrementor(4) # returns 5

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This section provided an overview of keywords in Python and their specific uses. Keywords are fundamental building blocks of Python syntax, and knowing them is key to mastering the language. 🚀