Learn Python

• check python version
  python --ver or python3 --ver
• to enter python
  python or python3 or python3.<version> or python2.<version>
• after enter to python, type help() to get help
  >>>help() or help('modules') or help('<modules_name>') e.g. help('paramiko') or help('<modules_name>.<class_name>') e.g. help('getpass.getpass')
also without entering python, can use:
pydoc <moudule> or pydoc <module>.<class>
• to list the modules
  help>modules
• Create virtual environment: install using pip
  pip install virtualenv or pip3 install virtualenv
Create virtualenv directory: virtualenv <directory_name>
Activate virtualenv: source <directory_name>/bin/activate
The prompt now will begin with <directory_name>.
• Virtual environment to use python 2.7
  virtualenv -p /usr/bin/python2.7 <new_venv>
• input
  var_as_st = raw_input('some words')
var_python_will_chose_best_type = input('some words')
but in python 3.x, we need to add int before the input:
  var = int(input("something"))
raw_input also not available anymore in python3.x
• Output
  python2.x : print var
python3.x : print(var)
if need to decode the ascii: print(var.decode(‘ascii’)
• Write
  python2.x: var.write(“something”)
  python3.x: var.write(b”something”)
  where b means byte
  to read from input:
  python3.x:
  var.write(var_input.encode(‘ascii’))
• Comment: use #
• Variable type: >>>type(var)
• List of operation to a variable: >>>dir(var)
• PEP: Python Enhancement Proposals
  - single quote(‘) and double quote(“) are same
  - indentation: use 4 spaces. e.g. all lines after IF with indentation are clause if IF true (or false)
  - be consistent: tab, then all tab. Space then all spaces

Source: Youtube

Error

• ImportError: cannot import name
  This is if the filename is same as library/module name.

$ python2.7 python/telnetlib.py
Traceback (most recent call last):
File "python/telnetlib.py", line 2, in <module>
from telnetlib import Telnet
File "/home/damha/python/telnetlib.py", line 2, in <module>
from telnetlib import Telnet