Lexical Analysis
Line Structure |
Joining Lines |
Blank Lines |
Comments |
Encoding Declaration |
Indentation |
Input and Output
Printing output |
print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False) |
print("Hello world!", end=" ") |
Getting input |
input([prompt]) |
input("Enter your age") |
Indentation
Leading whitespace (spaces and tabs) at the beginning of a logical line is used to compute the indentation level of the line, which in turn is used to determine the grouping of statements. |
Encoding Declaration
If a comment in the first or second line of the Python script matches the regular expression, this comment is processed as an encoding declaration; the first group of this expression names the encoding of the source code file. |
#!/usr/bin/env python
# -*- coding: utf-8 -*- |
Comments
Hash |
# |
# some comment |
DocString |
""" """ |
"""Demonstrates docstrings and does nothing really.""" |
Blank Lines
A logical line that contains only spaces, tabs, formfeeds and possibly a comment, is ignored. |
During interactive input of statements, handling of a blank line may differ depending on the implementation of the read-eval-print loop. |
In the standard interactive interpreter, an entirely blank logical line terminates a multi-line statement. |
Joining Lines
Explicit line joining |
Two or more physical lines may be joined into logical lines using backslash characters (\), as follows: when a physical line ends in a backslash that is not part of a string literal or comment, it is joined with the following forming a single logical line, deleting the backslash and the following end-of-line character. |
if 1900 < year < 2100 and 1 <= month <= 12 \ and 1 <= day <= 31 and 0 <= hour < 24 \ and 0 <= minute < 60 and 0 <= second < 60: # Looks like a valid date return 1 |
Implicit line joining |
Expressions in parentheses, square brackets or curly braces can be split over more than one physical line without using backslashes. |
month_names =
['Januari', 'Februari', 'Maart', # These are the
'April', 'Mei', 'Juni', # Dutch names 'Juli', 'Augustus', 'September', # for the months 'Oktober', 'November', 'December'] # of the year |
Remember:
-> A line ending in a backslash cannot carry a comment.
-> A backslash does not continue a comment.
-> A backslash does not continue a token except for string literals (i.e., tokens other than string literals cannot be split across physical lines using a backslash).
-> A backslash is illegal elsewhere on a line outside a string literal.
Line Structure
Logical Lines |
A logical line is what Python sees as a single statement |
Here is one logical on a physical line:
1) my_list = [1, 2, 3, 4]
2) print("Hello world!") |
Physical Lines |
A physical line is what you see when you write the program. Two or more physical lines may be joined into logical lines using backslash characters. |
Here is one logical line on two physical lines:
1) my_list = [1, 2,
3, 4]
2) s = 'This is a string. \ This continues the string.' |
Introduction
Founder |
Guido van Rossum |
First release |
February 20, 1991 |
Developers |
Python Software Foundation |
Paradigm |
Multi-paradigm: functional, imperative, object-oriented, structured, reflective |
Type Discipline |
Duck, dynamic, gradual |
Language Type |
Interpreted |
|
|
Identifiers
Lu - uppercase letters |
A..Z |
UPPERCASENAME |
Ll - lowercase letters |
a...z |
LOWERCASENAME |
Lt - titlecase letters |
a..zA..z |
titleCaseName |
Nl - letter numbers |
a...zA...z1...n |
name2000 | NAME999 |
Pc - connector punctuations |
a_zA_Z |
name_connector | NAME_CONNECTOR |
A Python identifier is a name used to identify a variable, function, class, module or other object.
Identifier naming standards are mentioned above.
Keywords and Reserved words
False |
await |
else |
import |
pass |
None |
break |
except |
in |
raise |
True |
class |
finally |
is |
return |
and |
continue |
for |
lambda |
try |
as |
def |
from |
nonlocal |
while |
assert |
del |
global |
not |
with |
async |
elif |
if |
or |
yield |
Keywords cannot be used as ordinary identifiers.
Variables
Definition |
Variable is a reserved memory location to store values |
Syntax |
IDENTIFIER_NAME = VALUE(1) |
Assignment Operator |
= |
Walrus Operator/Assignment Expressions |
:= |
Example |
number = 10 | name = "Some name" | print(walrus := True) |
Multiple Assignment |
a = b = c = 1 | a,b,c = 1,2,"john" |
Deleting variable |
del VARIABLE_NAME |
(1) VALUE => any built-in type or user-defined class or function
Built-in Types
Boolean types |
Truthy Falsy values |
Scalar |
Numeric types |
Integer, Float, Complex |
Scalar |
Sequence types |
List, Tuple, Range |
Compound |
Text Sequence types |
String |
Scalar |
Mapping types |
dictionary |
Compound |
Binary Sequence types |
bytes, bytesarray, memoryview |
Compound |
Set types |
set, frozenset |
Compound |
Other types |
functions, modules, class, methods, code objects, type objects, elipsis object, null object, notImplemented objects |
Special attributes |
Numeric Type
Integer |
Link |
Float |
Link |
Complex |
Link |
Sequence Types
Common sequence operations |
Link |
List |
Link |
Tuple |
Link |
Range |
LInk |
String |
Link |
Binary Sequence Types
Bytes |
Link |
Bytesarray |
Link |
Memoryview |
Link |
Other Types
Functions |
Link |
Class |
Link |
Modules |
Link |
Elipsis |
Link |
Null |
Link |
NotImplemented |
Link |
Special Attributes |
Link |
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