Python

Popularity of Python:

Python is general purpose programming language.

Python is adopted in scientific computing and machine learning areas.

The Zen of Python

Beautiful is better than ugly.

Explicit is better than implicit.

Simple is better than complex.

Complex is better than complicated.

Flat is better than nested.

Sparse is better than dense.

Readability counts.

Special cases aren't special enough to break the rules.

Although practicality beats purity.

Errors should never pass silently.

Unless explicitly silenced.

In the face of ambiguity, refuse the temptation to guess.

There should be one-- and preferably only one --obvious way to do it.

Although that way may not be obvious at first unless you're Dutch.

Now is better than never.

Although never is often better than *right* now.

If the implementation is hard to explain, it's a bad idea.

If the implementation is easy to explain, it may be a good idea.

Namespaces are one honking great idea -- let's do more of those!

 ~ Tim Peters

Python Standard Types

  • Numeric type: int - no decimal points; int_var = 5
  • Numeric type: float - real numbers with decimal points; flt_var = 7.4
  • String - sequence of characters; str_var = 'str'
  • List - mutable, stores multiple members; list_vaar = [1, 2.5, 'str']
  • Tuple - immutable, stores multiple members; tpl_var = (2, 4.7, 'abc')
  • Dictionary - key-value pairs; dict_var = {'planet': 'Mars', 'population': 0}

SUFFIXES = {1000: ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'],

	1024: ['KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB']}

	

def approximate_size(size, kilobyte_is_1024_bytes=True):

	'''Convert a file size to human-readable form.

	Keyword arguments:

	size -- file size in bytes

	kilobyte_is_1024_bytes -- if True (default), use multiples of 1024

	if False, use multiples of 1000

	Returns: string

	'''

	if size < 0:

		raise ValueError('number must be non-negative')

	multiple = 1024 if kilobyte_is_1024_bytes else 1000

	for suffix in SUFFIXES[multiple]:

		size /= multiple

		if size < multiple:

			return '{0:.1f} {1}'.format(size, suffix)

	raise ValueError('number too large')





approximate_size(1000000000000, False) # 1.0 TB

approximate_size(1000000000000) # 931.3 GiB

approximate_size(size=4000, kilobyte_is_1024_bytes=False) # 4.0 KB

approximate_size(kilobyte_is_1024_bytes=False, size=4000) # 4.0 KB

Working with string

Convert to string (Casting to string)


str(77)

Convert to integer


int('77')

Convert to float


float('7.7')

Check types


isinstance([], list) # True

isinstance({}, dict) # True

isinstance('', str) # True

type(requested_page)

type([]) is list # True

type({}) is dict # True

type('') is str # True

type(0) is int # True

type({}) # <type 'dict'>

type([]) # <type 'list'>

Logging


import logging

logging.warn('warning')

if-elif-else-endif in Jinja templates


{% if kenny.sick %}

    Kenny is sick.

{% elif kenny.dead %}

    You killed Kenny! You bastard!!!

{% else %}

    Kenny looks okay. So far.

{% endif %}

While:


while True:

    print('Username:')

    username = raw_input()

    if username != 'jack':

        continue

    print('Hello, Jack. What is the password?')

    password = raw_input()

    if password == 'aloha':

        break

print('Access granted.')

Clear session:


self.session.pop('session_data', None)

Safe conversion to int (safe int casting):


card_amount = self.request.POST.get('card_amount', 0)

try:

	card_amount = int(card_amount)

except(ValueError, TypeError):

	card_amount = 0

Delete all text files


import os

for filename in os.listdir():

    if filename.endswith('.txt'):

        os.unlink(filename)

Pythonic way


# Looping over a range of numbers



for i in [0, 1, 2, 3, 4, 5]:

    print i**2



# Looping over a range of numbers in a pythonic way

	

for i in range(6):

    print i**2

	

	

# Looping over a collection



colors = ['red', 'green', 'blue']

for i in range(len(colors)):

    print colors[i]

	

# Looping over a collection in a pythonic way

	

colors = ['red', 'green', 'blue']

for color in colors:

    print color



	

# Looping backwards



colors = ['red', 'green', 'blue']

for i in range(len(colors)-1, -1, -1):

    print colors[i]

	

# Looping backwards in a pythonic way



colors = ['red', 'green', 'blue']

for color in reversed(colors):

    print color



	

# Looping over a collection and indicies



colors = ['red', 'green', 'blue']

for i in range(len(colors)):

    print i, '-->', colors[i]

	

# Looping over a collection and indicies in a pythonic way

	

colors = ['red', 'green', 'blue']

for i, color in enumerate(colors):

    print i, '-->', color

	

	

# Looping in sorted order in a pythonic way



colors = ['red', 'green', 'blue']

for color in sorted(colors):

    print color

	

# Looping in sorted reversed order in a pythonic way



colors = ['red', 'green', 'blue']

for color in sorted(colors, reverse=True):

    print color





# Function calls with keyword arguments



twitter_search('@tesla', False, 20, True)



# Function calls with keyword arguments in a pythonic way



twitter_search('@tesla', retweets=False, numtweets=20, popular=True)





# Concatenating strings



colors = ['red', 'green', 'blue']

s = colors[0]

for color in colors[1:]:

    s += ', ' + color

print s



# Concatenating strings in a pythonic way



colors = ['red', 'green', 'blue']

print ', '.join(colors)



import antigravity

# opens browser with custom URL

================


pip install virtualenvwrapper-win

mkvirtualenv myproject

workon myproject

cd /_django-dev/

django-admin startproject devsite

cd devsite

python manage.py runserver

python manage.py migrate

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