Lexical Structure

Python is very particular about program layout, especially with regard to lines and indentation.

Lines and Indentation

In Python, the end of a physical line marks the end of most statements. Unlike in othe programming languages such as C, C++, Python statements are not normally terminated with a delimiter, such as a semicolon (;).
When a statement is too long to fit on a single physical line, you can join two adjacent physical lines into a logical line by ensuring that the first physical line has no comment and ends with a backslash (\)
Python also joins adjacent physical lines into one logical line if an open parenthesis((), bracket ([), or brace ({) has not yet been closed.
Python uses indentation to express the block structure of a program. Unlike other languages, Python does not use braces or being/end delimiters around blocks of statements:
- Indentation is the only way to indicate such blocks
- All statements in a block must have the same indentation
- Python style is to use four spaces per indentation level

An identifier is a name used to identify a variable, function, class, module, or other object.
Normal Python style is to start class names with an uppercase letter and other identifiers with a lowercase letter.
Starting an identifier with a single leading underscore indicates by convention that the identifier is meant to be private.
Starting an identifier with two leading underscores indicates a strongly private identifier; if the identifier also ends with two trailing underscores, the identifier is a language-defined special name.
The identifier _ (a single underscore) is special in interactive interpreter sessions: the interpreter binds _ to the result of the last expression statement evaluated interactively, if any.

Python version 3+ has a set of 33 keywords that are reserved words that cannot be used as variable names, function names, or any other identifiers:

Method	Description
and	A logical operator
as	To create an alias
assert	For debugging
break	To break out of a loop
class	To define a class
continue	To continue to the next iteration of a loop
def	To define a function
del	To delete an object
elif	Used in conditional statements, same as else if
else	Used in conditional statements
except	Used with exceptions, what to do when an exception occurs
False	Boolean value, result of comparison operations
finally	Used with exceptions, a block of code that will be executed no matter if there is an exception or not
for	To create a for loop
from	To import specific parts of a module
global	To declare a global variable
if	To make a conditional statement
import	To import a module
in	To check if a value is present in a list, tuple, etc.
is	To test if two variables are equal
lambda	To create an anonymous function
None	Represents a null value
nonlocal	To declare a non-local variable
not	A logical operator
or	A logical operator
pass	A null statement, a statement that will do nothing
raise	To raise an exception
return	To exit a function and return a value
True	Boolean value, result of comparison operations
try	To make a try…except statement
while	To create a while loop
with	Used to simplify exception handling
yield	To end a function, returns a generator