Skip to content

Introduction

Cmdloop

Source code :

#!/usr/bin/env python3
from cmd import Cmd


class Term(Cmd):
    prompt = ">>> "

    def default(self, args):
        print(args)

    def do_exit(self, args):
        return True


if __name__ == "__main__":
    term = Term()
    term.cmdloop()

Execution :

$ python3 loop.py
>>> hello world !
hello world !
>>> exit

Basic information

Wiki :

  • First appeared : February 20, 1991
  • Author : Guido van Rossum

Principle :

  • Interpreted
  • High-level
  • Garbage collector
  • Dynamically-typed
  • Multi-paradigm

Paradigm :

  • Object-oriented
  • Procedural (imperative)
  • Functional
  • Structured
  • Reflective

Why python ?

  • Open Source
  • Wide community
  • Easy to learn

Interpreter :

Source (.py) -> Compilation -> Bytecode (.pyo) -> Interpreter -> Execution

2 modes :

  • REPL (Read, Eval, Print, Loop) - ex: IPython
  • Scripts - ex: example.py

Basic syntax

>>> print("hello world !")
hello world !

Variables

List

More docs.

>>> l1 = [1, 2, 3]
>>> l1.append(4)
>>> l1
[1, 2, 3, 4]
>>> del l1[1]
>>> l1
[1, 3, 4]
>>> len(l1)
3
>>> 4 in l1
True
>>> 2 in l1
False
>>> [0]*10
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

>>> l2 = ["infosec", 0xA, 32, "wiki"]
>>> for element in l2: print(element)
infosec
10
32
wiki

# Access with index (positive or negative)

>>> l1[0]
1
>>> l1[-1]
4
>>> l1[-2]
3

# list[start:end:step]

>>> l1[0:3]
[1, 2, 3]
>>> l1[:3]
[1, 2, 3]
>>> l1[3:]
[4]
>>> l1[::2]
[1, 3]
>>> l1[:]
[1, 2, 3, 4]

Dict

Set

Frozenset

Magic methods

Introduction

Magic methods are called under the hood and can be redefined by the developer.

__add__

# Implementation already defined in the Integer class

>>> 5+3
8
>>> (5).__add__(3)
8

# User implementation of "+" comportment

>>> class Num:
...     def __init__(self, number):
...             self.number = number
...     def __add__(self, obj):
...             return Num(self.number + obj.number)
...
>>> num1 = Num(5)
>>> num2 = Num(10)
>>> num3 = num1 + num2
>>> num3.number
15

__str__

class Employee:

    def __init__(self):

        self.name = "xanhacks"
        self.salary = 10000

class SuperEmployee(Employee):

    def __str__(self):
        return f"Name: {self.name}, Salary: {self.salary}"

e = Employee()
print(e)

se = SuperEmployee()
print(se)
<__main__.Employee object at 0x7f5cdff8c730>
Name: xanhacks, Salary: 10000

Mutable / Immutable

Mutable Immutable
Lists Numbers (Integer, Rational, Float, Decimal, Complex, Booleans)
Sets Strings
Dictionaries Tuples
Frozen Sets

User-Defined Classes can be mutable or immutable depending on the class.

Integer (Immutable)

There will be only one Integer object with a specific value of X thanks to cache optimization.

>>> var1 = 50
>>> var2 = 50
>>> id(var1)
140386274742096
>>> id(var2)
140386274742096

>>> var1 = 30
>>> var2
50
>>> id(var1) == id(var2)
False

>>> var1 = 50
>>> id(var1) == id(var2)
True

List (mutable)

>>> l1 = [1, 2, 3]
>>> l2 = l1
>>> l2.append(4)
>>> l1
[1, 2, 3, 4]
>>> l2
[1, 2, 3, 4]
>>> l1 == l2
True
>>> id(l1) == id(l2)
True

Built-in function

dir

dir(...)
    dir([object]) -> list of strings

    If called without an argument, return the names in the current scope.
    Else, return an alphabetized list of names comprising (some of) the attributes
    of the given object, and of attributes reachable from it.
>>> dir(int)
['__abs__', '__add__', '__and__', '__bool__', '__ceil__', '__class__', '__delattr__', '__dir__', '__divmod__', '__doc__', '__eq__', '__float__', '__floor__', '__floordiv__', '__format__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__init__', '__init_subclass__', '__int__', '__invert__', '__le__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__round__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'as_integer_ratio', 'bit_length', 'conjugate', 'denominator', 'from_bytes', 'imag', 'numerator', 'real', 'to_bytes']
Back to top