IPython: Another Python REPL interpreter

IPython is a neat alternative of Python's builtin REPL (Read–Eval–Print Loop) interpreter, also a kernel of Jupyter.

ref:
https://ipython.org/
https://jupyter.org/

Useful Commands

# cheatsheet
%quickref

# show details of any objects (including modules, classes, functions and variables)
random?
os.path.join?
some_variable?

# show source code of any objects
os.path.join??

# show nothing for a function that is not implemented in Python
len??

# run some shell commands directly in IPython
pwd
ll
cd
cp
rm
mv
mkdir new_folder

# run any shell command with ! prefix
!ls
!ping www.google.com
!youtube-dl

# assign command output to a variable
contents = !ls
print(contents)

ref:
http://ipython.readthedocs.io/en/stable/interactive/tutorial.html

Magic Functions

# list all magic functions
%lsmagic

# run a Python script and load objects into current session
%run my_script.py

# run a profiling for multi-line code
%%timeit
array = []
for i in xrange(100):
    array.append(i)

# paste multi-line code
%paste
%cpaste

# explore objects
%pdoc some_object
%pdef some_object
%psource some_object
%pfile some_object

# if you call it after hitting an exception, it will automatically open ipdb at the point of the exception
%debug

# the In object is a list which keeps track of the commands in order
print(In)

# the Out object is a dictionary mapping input numbers to their outputs
pinrt(Out)
print(Out[2], _2)

ref:
http://ipython.readthedocs.io/en/stable/interactive/magics.html
https://www.safaribooksonline.com/library/view/python-data-science/9781491912126/ch02.html