Python

Documentation

pydoc3 -b

Running Time

import time
start_time = time.time()
code...
t = time.time() - start_time
print("Total Elapsed Time of Running Program: {:.2f} seconds.".format(t))

Default Argument

import sys

if 2 == len(sys.argv):
    file_name = sys.argv[1]
else:
    file_name = '/home/aavloni/Desktop/Python_II/trees.dat'

Sort By Key

def second(obj):
  return obj[1]

x.sort(key=second)

Identity vs Equality

Identity: a is b
Equality: a == b
Show ID: hex(id(b))
Immutable (int, strings, etc...) assignment through '=' Aliases
Mutable (lists, etc...) assignment through '=' Copies

Copying Lists

creates an alias
new_list = existing_list
creates a new list*
new_list = list(existing_list)
creates a new list*
new_list = existing_list[:]

* only works on single dimension lists

Get / Change Type of Object

type(a)
list(a)
isinstance(a, (float, int))

Sort in place vs Sort as copy

In place: list_name.sort()
As copy: sorted(list_name)

Generic Exception

try:
    something()
except Exception as e:

len vs sizeof()

len returns number of elements
sys.sizeof() returns number of bytes

Tuple Benefits

Saves memory with multiple identical objects because of immutability.
Can be used as dictionary keys (hashable because tuples are immutable).
Can be used to unpack things, eg. a,b = b,a
Can be used to create a function with variable number of arguments:
def fn(*args)