Comprehensive Python Cheatsheet

Download text file or Fork me on GitHub.

Monty Python

Main#

if __name__ == '__main__':
    main()

List#

<list> = <list>[from_inclusive : to_exclusive : step_size]
<list>.append(<el>)
<list>.extend(<list>)
<list> += [<el>]
<list> += <list>
<list>.sort()
<list>.reverse()
<list> = sorted(<list>)
<iter> = reversed(<list>)
sum_of_elements  = sum(<list>)
elementwise_sum  = [sum(pair) for pair in zip(list_a, list_b)]
sorted_by_second = sorted(<list>, key=lambda el: el[1])
sorted_by_both   = sorted(<list>, key=lambda el: (el[1], el[0]))
flattened_list   = list(itertools.chain.from_iterable(<list>))
list_of_chars    = list(<str>)
product_of_elems = functools.reduce(lambda out, x: out * x, <list>)
index = <list>.index(<el>)  # Returns first index of item. 
<list>.insert(index, <el>)  # Inserts item at index and moves the rest to the right.
<el> = <list>.pop([index])  # Removes and returns item at index or from the end.
<list>.remove(<el>)         # Removes first occurrence of item.
<list>.clear()              # Removes all items.   

Dictionary#

<view>  = <dict>.keys()
<view>  = <dict>.values()
<view>  = <dict>.items()
<value> = <dict>.get(key, default)         # Returns default if key does not exist.
<value> = <dict>.setdefault(key, default)  # Same, but also adds default to dict.
<dict>.update(<dict>)
collections.defaultdict(<type>)     # Creates a dictionary with default value of type.
collections.defaultdict(lambda: 1)  # Creates a dictionary with default value 1.
collections.OrderedDict()           # Creates ordered dictionary.
dict(<list>)                        # Initiates a dict from list of key-value pairs.
dict(zip(keys, values))             # Initiates a dict from two lists.
{k: v for k, v in <dict>.items() if k in <list>}  # Filters a dict by keys.

Counter

>>> from collections import Counter
>>> colors = ['blue', 'red', 'blue', 'yellow', 'blue', 'red']
>>> Counter(colors)
Counter({'blue': 3, 'red': 2, 'yellow': 1})
>>> <counter>.most_common()[0][0]
'blue'

Set#

<set> = set()
<set>.add(<el>)
<set>.update(<set>)
<set>.clear()
<set>  = <set>.union(<set>)                 # Or: <set> | <set>
<set>  = <set>.intersection(<set>)          # Or: <set> & <set>
<set>  = <set>.difference(<set>)            # Or: <set> - <set>
<set>  = <set>.symmetric_difference(<set>)  # Or: <set> ^ <set>
<bool> = <set>.issubset(<set>)
<bool> = <set>.issuperset(<set>)

Frozenset

Is hashable and can be used as a key in dictionary.

<frozenset> = frozenset(<collection>)

Range#

range(to_exclusive)
range(from_inclusive, to_exclusive)
range(from_inclusive, to_exclusive, step_size)
range(from_inclusive, to_exclusive, -step_size)
from_inclusive = <range>.start
to_exclusive   = <range>.stop

Enumerate#

for i, <el> in enumerate(<collection> [, i_start]):
    ...

Named Tuple#

>>> Point = collections.namedtuple('Point', ['x', 'y'])
>>> a = Point(1, y=2)
Point(x=1, y=2)
>>> a.x
1
>>> getattr(a, 'y')
2
>>> Point._fields
('x', 'y')

Iterator#

Skips first element:

next(<iter>)
for element in <iter>:
    ...

Reads input until it reaches an empty line:

for line in iter(input, ''):
    ...

Same, but prints a message every time:

from functools import partial
for line in iter(partial(input, 'Please enter value'), ''):
    ...

Generator#

Convenient way to implement the iterator protocol.

def step(start, step):
    while True:
        yield start
        start += step
>>> stepper = step(10, 2)
>>> next(stepper), next(stepper), next(stepper)
(10, 12, 14)

Type#

<type> = type(<el>)  # <class 'int'> / <class 'str'> / ...
from numbers import Number, Integral, Real, Rational, Complex
is_number   = isinstance(<el>, Number)
is_function = callable(<el>)

String#

<str>  = <str>.strip()           # Strips all whitespace characters.
<str>  = <str>.strip('<chars>')  # Strips all passed characters.
<list> = <str>.split()                       # Splits on any whitespace character.
<list> = <str>.split(sep=None, maxsplit=-1)  # Splits on 'sep' at most 'maxsplit' times.
<str>  = <str>.join(<list>)                  # Joins elements using string as separator.
<str>  = <str>.replace(old_str, new_str)
<bool> = <str>.startswith(<sub_str>)      # Pass tuple of strings for multiple options.
<bool> = <str>.endswith(<sub_str>)        # Pass tuple of strings for multiple options.
<int>  = <str>.index(<sub_str>)           # Returns first index of a substring.
<bool> = <str>.isnumeric()                # True if str contains only numeric characters.
<list> = textwrap.wrap(<str>, width)      # Nicely breaks string into lines.

Char

<str> = chr(<int>)  # Converts int to unicode char.
<int> = ord(<str>)  # Converts unicode char to int.
>>> ord('0'), ord('9')
(48, 57)
>>> ord('A'), ord('Z')
(65, 90)
>>> ord('a'), ord('z')
(97, 122)

Print

print(<el_1> [, <el_2>, end='', sep='', file=<file>])  # Use 'file=sys.stderr' for errors.

Regex#

import re
<str>   = re.sub(<regex>, new, text, count=0)  # Substitutes all occurrences.
<list>  = re.findall(<regex>, text)
<list>  = re.split(<regex>, text, maxsplit=0)  # Use brackets in regex to keep the matches.
<Match> = re.search(<regex>, text)             # Searches for first occurrence of pattern.
<Match> = re.match(<regex>, text)              # Searches only at the beginning of the text.
<Match_iter> = re.finditer(<regex>, text)      # Searches for all occurrences of pattern.

Match Object

<str> = <Match>.group()   # Whole match.
<str> = <Match>.group(1)  # Part in first bracket.
<int> = <Match>.start()   # Start index of a match.
<int> = <Match>.end()     # Exclusive end index of a match.

Special Sequences

Use capital letter for negation.

'\d' == '[0-9]'          # Digit
'\s' == '[ \t\n\r\f\v]'  # Whitespace
'\w' == '[a-zA-Z0-9_]'   # Alphanumeric

Format#

<str> = f'{<el_1>}, {<el_2>}'
<str> = '{}, {}'.format(<el_1>, <el_2>)
>>> Person = namedtuple('Person', 'name height')
>>> person = Person('Jean-Luc', 187)
>>> f'{person.height:10}'
'       187'
>>> '{p.height:10}'.format(p=person)
'       187'

General Options

{<el>:<10}   # '<el>      '
{<el>:>10}   # '      <el>'
{<el>:^10}   # '   <el>   '
{<el>:->10}  # '------<el>'
{<el>:>0}    # '<el>'

Options Specific to Strings

{'abcde':.3}    # 'abc'
{'abcde':10.3}  # 'abc       '

Options specific to Numbers

{1.23456:.3f}    # '1.235'
{1.23456:10.3f}  # '     1.235'
{123456:10,}     # '   123,456'
{123456:10_}     # '   123_456'
{3:08b}          # '00000011' -> Binary with leading zeros.
{3:0<8b}         # '11000000' -> Binary with trailing zeros.

Float presentation types:

Integer presentation types:

Numbers#

Basic Functions

round(<num> [, ndigits])
abs(<num>)
math.pow(x, y)  # Or: x ** y

Constants

from math import e, pi

Trigonometry

from math import cos, acos, sin, asin, tan, atan, degrees, radians

Logarithm

from math import log, log10, log2
log(x [, base])  # Base e, if not specified.
log10(x)         # Base 10.
log2(x)          # Base 2.

Infinity, nan

from math import inf, nan, isfinite, isinf, isnan

Or:

float('inf'), float('nan')

Random

from random import random, randint, choice, shuffle
<float> = random()
<int>   = randint(from_inclusive, to_inclusive)
<el>    = choice(<list>)
shuffle(<list>)

Datetime#

from datetime import datetime, strptime
now = datetime.now()
now.month                      # 3
now.strftime('%Y%m%d')         # '20180315'
now.strftime('%Y%m%d%H%M%S')   # '20180315002834'
<datetime> = strptime('2015-05-12 00:39', '%Y-%m-%d %H:%M')

Arguments#

"*" is the splat operator, that takes a list as input, and expands it into actual positional arguments in the function call.

args   = (1, 2)
kwargs = {'x': 3, 'y': 4, 'z': 5}
func(*args, **kwargs)  

Is the same as:

func(1, 2, x=3, y=4, z=5)

Splat operator can also be used in function declarations:

def add(*a):
    return sum(a)
>>> add(1, 2, 3)
6

And in few other places:

>>> a = (1, 2, 3)
>>> [*a]
[1, 2, 3]
>>> head, *body, tail = [1, 2, 3, 4]
>>> body
[2, 3]

Inline#

Lambda

lambda: <return_value>
lambda <argument_1>, <argument_2>: <return_value>

Comprehension

<list> = [i+1 for i in range(10)]         # [1, 2, ..., 10]
<set>  = {i for i in range(10) if i > 5}  # {6, 7, ..., 9}
<dict> = {i: i*2 for i in range(10)}      # {0: 0, 1: 2, ..., 9: 18}
<iter> = (x+5 for x in range(10))         # (5, 6, ..., 14)
out = [i+j for i in range(10) for j in range(10)]

Is the same as:

out = []
for i in range(10):
    for j in range(10):
        out.append(i+j)

Map, Filter, Reduce

from functools import reduce
<iter>     = map(lambda x: x + 1, range(10))          # (1, 2, ..., 10)
<iter>     = filter(lambda x: x > 5, range(10))       # (6, 7, ..., 9)
<any_type> = reduce(lambda sum, x: sum+x, range(10))  # 45

Any, All

<bool> = any(el[1] for el in <collection>)

If - Else

<expression_if_true> if <condition> else <expression_if_false>
>>> [a if a else 'zero' for a in (0, 1, 0, 3)]
['zero', 1, 'zero', 3]

Namedtuple, Enum, Class

from collections import namedtuple
Point = namedtuple('Point', 'x y')

from enum import Enum
Direction = Enum('Direction', 'n e s w')
Cutlery = Enum('Cutlery', {'knife': 1, 'fork': 2, 'spoon': 3})

# Warning: Objects will share the objects that are initialized in the dictionary!
Creature = type('Creature', (), {'position': Point(0, 0), 'direction': Direction.n})
creature = Creature()

Closure#

def get_multiplier(a):
    def out(b):
        return a * b
    return out
>>> multiply_by_3 = get_multiplier(3)
>>> multiply_by_3(10)
30

Or:

from functools import partial
partial(<function>, <arg_1> [, <arg_2>, ...])

Decorator#

@closure_name
def function_that_gets_passed_to_closure():
    ...

Debugger example:

from functools import wraps

def debug(func):
    @wraps(func)  # Needed for metadata copying (func name, ...).
    def out(*args, **kwargs):
        print(func.__name__)
        return func(*args, **kwargs)
    return out

@debug
def add(x, y):
    return x + y

Class#

class <name>:
    def __init__(self, a):
        self.a = a
    def __str__(self):
        return str(self.a)
    def __repr__(self):
        return str({'a': self.a})  # Or: return f'{self.__dict__}'

    @classmethod
    def get_class_name(cls):
        return cls.__name__

Constructor Overloading

class <name>:
    def __init__(self, a=None):
        self.a = a

Copy

from copy import copy, deepcopy
<object> = copy(<object>)
<object> = deepcopy(<object>)

Enum#

from enum import Enum, auto
class <enum_name>(Enum):
    <member_name_1> = <value_1>  
    <member_name_2> = <value_2_a>, <value_2_b>
    <member_name_3> = auto()  # Can be used for automatic indexing.
    ...

   @classmethod
   def get_names(cls):
      return [a.name for a in cls.__members__.values()]

   @classmethod
   def get_values(cls):
      return [a.value for a in cls.__members__.values()]
<member>  = <enum>.<member_name>
<member>  = <enum>['<member_name>']
<member>  = <enum>(<value>)
<name>    = <member>.name
<value>   = <member>.value
list_of_members = list(<enum>)
member_names    = [a.name for a in <enum>]
random_member   = random.choice(list(<enum>))

Inline

Cutlery = Enum('Cutlery', ['knife', 'fork', 'spoon'])
Cutlery = Enum('Cutlery', 'knife fork spoon')
Cutlery = Enum('Cutlery', {'knife': 1, 'fork': 2, 'spoon': 3})

# Functions can not be values, so they must be enclosed in tuple:
LogicOp = Enum('LogicOp', {'AND': (lambda l, r: l and r, ),
                           'OR' : (lambda l, r: l or r, )})

# But 'list(<enum>)' will only work if there is another value in the tuple:
LogicOp = Enum('LogicOp', {'AND': (auto(), lambda l, r: l and r),
                           'OR' : (auto(), lambda l, r: l or r)})

System#

Arguments

import sys
script_name = sys.argv[0]
arguments   = sys.argv[1:]

Read File

def read_file(filename):
    with open(filename, encoding='utf-8') as file:
        return file.readlines()

Write to File

def write_to_file(filename, text):
    with open(filename, 'w', encoding='utf-8') as file:
        file.write(text)

Path

import os
<bool> = os.path.exists(<path>)
<bool> = os.path.isfile(<path>)
<bool> = os.path.isdir(<path>)
<list> = os.listdir(<path>)

Execute Command

import os
<str> = os.popen(<command>).read()

Or:

>>> import subprocess
>>> a = subprocess.run(['ls', '-a'], stdout=subprocess.PIPE)
>>> a.stdout
b'.\n..\nfile1.txt\nfile2.txt\n'
>>> a.returncode
0

Input

filename = input('Enter a file name: ')

Prints lines until EOF:

while True:
    try:
        print(input())
    except EOFError:
        break

Recursion Limit

>>> sys.getrecursionlimit()
1000
>>> sys.setrecursionlimit(10000)

JSON#

import json

Serialization

<str>  = json.dumps(<object>, ensure_ascii=True, indent=None)
<dict> = json.loads(<str>)

To preserve order:

from collections import OrderedDict
<dict> = json.loads(<str>, object_pairs_hook=OrderedDict)

Read File

def read_json_file(filename):
    with open(filename, encoding='utf-8') as file:
        return json.load(file)

Write to File

def write_to_json_file(filename, an_object):
    with open(filename, 'w', encoding='utf-8') as file:
        json.dump(an_object, file, ensure_ascii=False, indent=2)

SQLite#

import sqlite3
db = sqlite3.connect(<filename>)

Read

cursor = db.execute(<query>)
if cursor:
    cursor.fetchall()  # Or cursor.fetchone()
db.close()

Write

db.execute(<query>)
db.commit()

Pickle#

import pickle
favorite_color = {'lion': 'yellow', 'kitty': 'red'}
pickle.dump(favorite_color, open('data.p', 'wb'))
favorite_color = pickle.load(open('data.p', 'rb'))

Exceptions#

while True:
    try:
        x = int(input('Please enter a number: '))
    except ValueError:
        print('Oops!  That was no valid number.  Try again...')
    else:
        print('Thank you.')
        break

Raising exception:

raise ValueError('A very specific message!')

Finally:

>>> try:
...     raise KeyboardInterrupt
... finally:
...     print('Goodbye, world!')
... 
Goodbye, world!
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
KeyboardInterrupt

Bytes#

Bytes objects are immutable sequences of single bytes.

Encode

<Bytes> = b'<str>'
<Bytes> = <str>.encode(encoding='utf-8')
<Bytes> = <int>.to_bytes(<length>, byteorder='big|little', signed=False)
<Bytes> = bytes.fromhex(<hex>)

Decode

<str> = <Bytes>.decode('utf-8') 
<int> = int.from_bytes(<Bytes>, byteorder='big|little', signed=False)
<hex> = <Bytes>.hex()

Read Bytes from File

def read_bytes(filename):
    with open(filename, 'rb') as file:
        return file.read()

Write Bytes to File

def write_bytes(filename, bytes):
    with open(filename, 'wb') as file:
        file.write(bytes)
<Bytes> = b''.join(<list_of_Bytes>)

Struct#

This module performs conversions between Python values and C struct represented as Python Bytes object.

<Bytes> = struct.pack('<format>', <value_1> [, <value_2>, ...])
<tuple> = struct.unpack('<format>', <Bytes>)

Example

>>> from struct import pack, unpack, calcsize
>>> pack('hhl', 1, 2, 3)
b'\x00\x01\x00\x02\x00\x00\x00\x03'
>>> unpack('hhl', b'\x00\x01\x00\x02\x00\x00\x00\x03')
(1, 2, 3)
>>> calcsize('hhl')
8

Format

Use capital leters for unsigned type.

Hashlib#

>>> hashlib.md5(<str>.encode()).hexdigest()
'33d0eba106da4d3ebca17fcd3f4c3d77'

Threading#

from threading import Thread, RLock

Thread

thread = Thread(target=<function>, args=(<first_arg>, ))
thread.start()
...
thread.join()

Lock

lock = Rlock()
lock.acquire()
...
lock.release()

Itertools#

Every function returns an iterator and can accept any collection and/or iterator. If you want to print the iterator, you need to pass it to the list() function.

from itertools import *

Combinatoric iterators

>>> combinations('abc', 2)
[('a', 'b'), ('a', 'c'), ('b', 'c')]

>>> combinations_with_replacement('abc', 2)
[('a', 'a'), ('a', 'b'), ('a', 'c'), 
 ('b', 'b'), ('b', 'c'), ('c', 'c')]

>>> permutations('abc', 2)
[('a', 'b'), ('a', 'c'), 
 ('b', 'a'), ('b', 'c'), 
 ('c', 'a'), ('c', 'b')]

>>> product('ab', [1, 2])
[('a', 1), ('a', 2), 
 ('b', 1), ('b', 2)]

>>> product([0, 1], repeat=3)
[(0, 0, 0), (0, 0, 1), (0, 1, 0), (0, 1, 1), 
 (1, 0, 0), (1, 0, 1), (1, 1, 0), (1, 1, 1)]

Infinite iterators

>>> i = count(5, 2)
>>> next(i), next(i), next(i)
(5, 7, 9)

>>> a = cycle('abc')
>>> [next(a) for _ in range(10)]
['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c', 'a']

>>> repeat(10, 3)
[10, 10, 10]

Iterators

>>> chain([1, 2], range(3, 5))
[1, 2, 3, 4]

>>> compress('abc', [True, 0, 1])
['a', 'c']

>>> islice([1, 2, 3], 1, None)  # islice(<seq>, from_inclusive, to_exclusive) 
[2, 3]

>>> people = [{'id': 1, 'name': 'bob'}, 
              {'id': 2, 'name': 'bob'}, 
              {'id': 3, 'name': 'peter'}]
>>> {name: list(ppp) for name, ppp in groupby(people, key=lambda p: p['name'])}
{'bob':   [{'id': 1, 'name': 'bob'}, 
           {'id': 2, 'name': 'bob'}], 
 'peter': [{'id': 3, 'name': 'peter'}]}

Introspection and Metaprograming#

Inspecting code at runtime and code that generates code. You can:

Variables

<list> = dir()      # In-scope variables.
<dict> = locals()   # Local variables.
<dict> = globals()  # Global variables.

Attributes

>>> class Z:
...     def __init__(self):
...             self.a = 'abcde'
...             self.b = 12345
>>> z = Z()
>>> getattr(z, 'a')  # Same as Z.__getattribute__(z, 'a')
'abcde'

>>> hasattr(z, 'c')
False

>>> setattr(z, 'c', 10)

Parameters

Getting the number of parameters of a function:

from inspect import signature
sig = signature(<function>)
no_of_params = len(sig.parameters)

Type

Type is the root class. If only passed the object it returns it's type. Otherwise it creates a new class (and not the instance!):

type(<class_name>, <parents_tuple>, <attributes_dict>)
>>> Z = type('Z', (), {'a': 'abcde', 'b': 12345})
>>> z = Z()

MetaClass

Class that creates class:

def my_meta_class(name, parents, attrs):
    ...
    return type(name, parents, attrs)

Or:

class MyMetaClass(type):
    def __new__(klass, name, parents, attrs):
        ...
        return type.__new__(klass, name, parents, attrs)

Metaclass Attribute

When class is created it checks if it has metaclass defined. If not, it recursively checks if any of his parents has it defined, and eventually comes to type:

class BlaBla:
    __metaclass__ = Bla

Operator#

from operator import add, sub, mul, truediv, floordiv, mod, pow, neg, abs, \
                     eq, ne, lt, le, gt, ge, \
                     not_, and_, or_, xor, \
                     itemgetter
from enum import Enum
from functools import reduce

product_of_elems = reduce(mul, <list>)
sorted_by_second = sorted(<list>, key=itemgetter(1))
sorted_by_both   = sorted(<list>, key=itemgetter(0, 1))
LogicOp          = Enum('LogicOp', {'AND': (and_, ),
                                    'OR' : (or_, )})

Eval#

Basic

>>> from ast import literal_eval
>>> literal_eval('1 + 1')
2
>>> literal_eval('[1, 2, 3]')
[1, 2, 3]

Detailed

from ast import parse, Num, BinOp, UnaryOp, \
                Add, Sub, Mult, Div, Pow, BitXor, USub
import operator as op

operators = {Add:    op.add, 
             Sub:    op.sub, 
             Mult:   op.mul,
             Div:    op.truediv, 
             Pow:    op.pow, 
             BitXor: op.xor,
             USub:   op.neg}

def evaluate(expression):
    root = parse(expression, mode='eval')
    return eval_node(root.body)

def eval_node(node):
    type_ = type(node)
    if type_ == Num:
        return node.n
    if type_ not in [BinOp, UnaryOp]:
        raise TypeError(node)
    operator = operators[type(node.op)]
    if type_ == BinOp:
        left, right = eval_node(node.left), eval_node(node.right)
        return operator(left, right)
    elif type_ == UnaryOp:
        operand = eval_node(node.operand)
        return operator(operand)
>>> evaluate('2^6')
4
>>> evaluate('2**6')
64
>>> evaluate('1 + 2*3**(4^5) / (6 + -7)')
-5.0

Coroutine#

Helper Decorator

def coroutine(func):
    def start(*args, **kwargs):
        cr = func(*args, **kwargs)
        next(cr)
        return cr
    return start

Pipeline Example

def reader(target):
    for i in range(10):
        target.send(i)
    target.close()

@coroutine
def adder(target):
    while True:
        item = (yield)
        target.send(item + 100)

@coroutine
def printer():
    while True:
        item = (yield)
        print(item)

reader(adder(printer()))



Libraries

Plot#

# $ pip3 install matplotlib
from matplotlib import pyplot
pyplot.plot(<data_1> [, <data_2>, ...])
pyplot.show()
pyplot.savefig(<filename>, transparent=True)

Table#

Prints CSV file as ASCII table:

# $ pip3 install tabulate
import csv
from tabulate import tabulate
with open(<filename>, newline='') as csv_file:
    reader = csv.reader(csv_file, delimiter=';')
    headers = [a.title() for a in next(reader)]
    print(tabulate(reader, headers))

Curses#

# $ pip3 install curses
from curses import wrapper

def main():
    wrapper(draw)

def draw(screen):
    screen.clear()
    screen.addstr(0, 0, 'Press ESC to quit.')
    while screen.getch() != 27:
        pass

def get_border(screen):
    from collections import namedtuple
    P = namedtuple('P', 'x y')
    height, width = screen.getmaxyx()
    return P(width - 1, height - 1)

Image#

Creates PNG image of greyscale gradient:

# $ pip3 install pillow
from PIL import Image
width, height = 100, 100
img = Image.new('L', (width, height), 'white')
img.putdata([255*a/(width*height) for a in range(width*height)])
img.save('out.png')

Modes

Audio#

Saves list of floats with values between 0 and 1 to a WAV file:

import wave, struct
frames = [struct.pack('h', int((a-0.5)*60000)) for a in <list>]
wf = wave.open(<filename>, 'wb')
wf.setnchannels(1)
wf.setsampwidth(4)
wf.setframerate(44100)
wf.writeframes(b''.join(frames))
wf.close()

Url#

from urllib.parse import quote, quote_plus, unquote, unquote_plus

Encode

>>> quote("Can't be in URL!")
'Can%27t%20be%20in%20URL%21'
>>> quote_plus("Can't be in URL!")
'Can%27t+be+in+URL%21'

Decode

>>> unquote('Can%27t+be+in+URL%21')
"Can't+be+in+URL!"'
>>> unquote_plus('Can%27t+be+in+URL%21')
"Can't be in URL!"

Web#

# $ pip3 install bottle
import bottle
from urllib.parse import unquote

Run

bottle.run(host='localhost', port=8080)
bottle.run(host='0.0.0.0', port=80, server='cherrypy')

Static request

@route('/img/<image>')
def send_image(image):
    return static_file(image, 'images/', mimetype='image/png')

Dynamic request

@route('/<sport>')
def send_page(sport):
    sport = unquote(sport).lower()
    page = read_file(sport)
    return template(page)

REST request

@post('/odds/<sport>')
def odds_handler(sport):
    team = bottle.request.forms.get('team')
    team = unquote(team).lower()

    db = sqlite3.connect(<db_path>)
    home_odds, away_odds = get_odds(db, sport, team)
    db.close()

    response.headers['Content-Type'] = 'application/json'
    response.headers['Cache-Control'] = 'no-cache'
    return json.dumps([home_odds, away_odds])

Profile#

Basic:

from time import time
start_time = time()
...
duration = time() - start_time

Times execution of the passed code:

from timeit import timeit
timeit('"-".join(str(n) for n in range(100))', 
       number=10000, globals=globals())

Generates a PNG image of call graph and highlights the bottlenecks:

# $ pip3 install pycallgraph
import pycallgraph
graph = pycallgraph.output.GraphvizOutput()
graph.output_file = get_filename()
with pycallgraph.PyCallGraph(output=graph):
    <code_to_be_profiled>
def get_filename():
    from datetime import datetime
    time_str = datetime.now().strftime('%Y%m%d%H%M%S')
    return f'profile-{time_str}.png'

Progress Bar#

Tqdm

# $ pip3 install tqdm
from tqdm import tqdm
from time import sleep
for i in tqdm(range(100)):
    sleep(0.02)
for i in tqdm([1, 2, 3]):
    sleep(0.2)

Basic

import sys

class Bar():
    @staticmethod
    def range(*args):
        bar = Bar(len(list(range(*args))))
        for i in range(*args):
            yield i 
            bar.tick()
    @staticmethod
    def foreach(elements):
        bar = Bar(len(elements))
        for el in elements:
            yield el
            bar.tick()
    def __init__(s, steps, width=40):
        s.st, s.wi, s.fl, s.i = steps, width, 0, 0
        s.th = s.fl * s.st / s.wi
        s.p(f"[{' ' * s.wi}]")
        s.p('\b' * (s.wi + 1))
    def tick(s):
        s.i += 1
        while s.i > s.th:
            s.fl += 1
            s.th = s.fl * s.st / s.wi
            s.p('-')
        if s.i == s.st:
            s.p('\n')
    def p(s, t):
        sys.stdout.write(t)
        sys.stdout.flush()

Usage:

from time import sleep
for i in Bar.range(100):
    sleep(0.02)
for el in Bar.foreach([1, 2, 3]):
    sleep(0.2)

Basic Script Template#

# Linux:
#!/usr/bin/env python3
# Mac:
#!/usr/local/bin/python3
#
# Usage: .py 
# 

from collections import namedtuple
from enum import Enum
import re
import sys


def main():
    pass


###
##  UTIL
#

def read_file(filename):
    with open(filename, encoding='utf-8') as file:
        return file.readlines()


if __name__ == '__main__':
    main()