Python Examples - cunhapaulo/ReferenceCard GitHub Wiki

Python language reference

0. Working with Filesystem

import os, path

main():

    file_type = "*.dll"
   
    my_path = Path("C:/WINDOWS/SYSTEM32")
    my_path.glob(file_type)
    list_dlls = list(my_path)

    pprint(list_dlls)

    ##
    ## More directly
    ##

    my_path = Path("C:/WINDOWS/SYSTEM32")
    list_dlls = list(my_path.glob("*.dll")) # Turns into List all files conforming to "*.dll"
    pprint(list_dlls)

1. Index

2. Data Structures

Nome Exemplo Odered Indexed Changeable Duplicates
List ["a", "b", "c"] yes yes yes yes
Dictionary {'nome': 'John', 'idade': 30} yes yes yes no
Tuple (1, 'dois', 3.0) yes yes no yes
Set {"apple", "banana", "cherry"} no no no no

2.1. List

image

  • Python will give you an IndexError error message if you use an index that exceeds the number of values in your list value.

2.1.1. Getting a List from Another List with Slices:

image

  • Getting a List’s Length with the len() Function
  • List Concatenation and List Replication with +
  • Removing Values from Lists with del Statements
    >>> spam = ['cat', 'bat', 'rat', 'elephant']
    >>> del spam[2]
    >>> spam
    ['cat', 'bat', 'elephant']
    >>> del spam[2]
    >>> spam
    ['cat', 'bat']

2.1.2. Program

catNames = []

while True:
    print('Enter the name of cat ' + str(len(catNames) + 1) +
          ' (Or enter nothing to stop.):')
    name = input()
    if name == '':
        break
    catNames = catNames + [name]  list concatenation

print('The cat names are:')
for name in catNames:
    print(' ' + name)

2.1.3. The in and not in Operators:

    myPets = ['Zophie', 'Pooka', 'Fat-tail']
    print('Enter a pet name:')
    name = input()
    if name not in myPets:
        print('I do not have a pet named ' + name)
    else:
        print(name + ' is my pet.')

2.1.4. The Multiple Assignment Trick

    >>> cat = ['fat', 'gray', 'loud']
    >>> size, color, disposition = cat

2.1.5. Using the enumerate() Function with Lists:

Instead of using the range(len(someList)) technique with a for loop to obtain the integer index of the items in the list, you can call the enumerate() function instead.

>>> supplies = ['pens', 'staplers', 'flamethrowers', 'binders']
>>> for index, item in enumerate(supplies):
... print('Index ' + str(index) + ' in supplies is: ' + item)
Index 0 in supplies is: pens
Index 1 in supplies is: staplers
Index 2 in supplies is: flamethrowers
Index 3 in supplies is: binders

Instead of using the range(len(someList)) technique with a for loop to obtain the integer index of the items in the list, you can call the enumerate() function instead. On each iteration of the loop, enumerate() will return two values: the index of the item in the list, and the item in the list itself.

2.1.6. Using the random.choice() and random.shuffle() Functions with Lists:

>>> import random
>>> pets = ['Dog', 'Cat', 'Moose']
>>> random.choice(pets)
'Dog'
>>> random.choice(pets)
'Cat'
>>> random.choice(pets)
'Cat'

------------------------------------------------------

>>> import random
>>> people = ['Alice', 'Bob', 'Carol', 'David']
>>> random.shuffle(people)
>>> people
['Carol', 'David', 'Alice', 'Bob']
>>> random.shuffle(people)
>>> people
['Alice', 'David', 'Bob', 'Carol']

2.1.7. Finding a Value in a List with the index() Method:

>>> spam = ['hello', 'hi', 'howdy', 'heyas']
>>> spam.index('hello')
0
>>> spam.index('heyas')
3
>>> spam.index('howdy howdy howdy')
Traceback (most recent call last):
File "<pyshell#31>", line 1, in <module>
spam.index('howdy howdy howdy')
ValueError: 'howdy howdy howdy' is not in list

Important: When there are duplicates of the value in the list, the index of its first appearance is returned.

2.1.8. Adding Values to Lists with the append() and insert() Methods:

>>> spam = ['cat', 'dog', 'bat']
>>> spam.append('moose')
>>> spam
['cat', 'dog', 'bat', 'moose']

------------------------------------------------

>>> spam = ['cat', 'dog', 'bat']
>>> spam.insert(1, 'chicken')
>>> spam
['cat', 'chicken', 'dog', 'bat']

2.1.9. Removing Values from Lists with the remove() Method:

>>> spam = ['cat', 'bat', 'rat', 'elephant']
>>> spam.remove('bat')
>>> spam
['cat', 'rat', 'elephant']

-------------------------------------------------

>>> spam = ['cat', 'bat', 'rat', 'elephant']
>>> spam.remove('chicken')
Traceback (most recent call last):
File "<pyshell#11>", line 1, in <module>
spam.remove('chicken')
ValueError: list.remove(x): x not in list

-------------------------------------------------

>>> spam = ['cat', 'bat', 'rat', 'cat', 'hat', 'cat']
>>> spam.remove('cat')
>>> spam
['bat', 'rat', 'cat', 'hat', 'cat']

2.1.10. Sorting the Values in a List with the sort() Method:

>>> spam = [2, 5, 3.14, 1, -7]
>>> spam.sort()
>>> spam
[-7, 1, 2, 3.14, 5]
>>> spam = ['ants', 'cats', 'dogs', 'badgers', 'elephants']
>>> spam.sort()
>>> spam
['ants', 'badgers', 'cats', 'dogs', 'elephants']

-------------------------------------------------

>>> spam.sort(reverse=True)
>>> spam
['elephants', 'dogs', 'cats', 'badgers', 'ants']

-------------------------------------------------

>>> spam = [1, 3, 2, 4, 'Alice', 'Bob']
>>> spam.sort()
Traceback (most recent call last):
File "<pyshell#70>", line 1, in <module>
spam.sort()
TypeError: '<' not supported between instances of 'str' and 'int'

-------------------------------------------------

>>> spam = ['Alice', 'ants', 'Bob', 'badgers', 'Carol', 'cats']
>>> spam.sort()
>>> spam
['Alice', 'Bob', 'Carol', 'ants', 'badgers', 'cats']

-------------------------------------------------

>>> spam = ['a', 'z', 'A', 'Z']
>>> spam.sort(key=str.lower)
>>> spam
['a', 'A', 'z', 'Z']

2.1.11. Reversing the Values in a List with the reverse() Method:

>>> spam = ['cat', 'dog', 'moose']
>>> spam.reverse()
>>> spam
['moose', 'dog', 'cat']

2.1.11.1. Program:

import random

 EXCEPTIONS TO INDENTATION RULES IN PYTHON
messages = ['It is certain',
    'It is decidedly so',
    'Yes definitely',
    'Reply hazy try again',
    'Ask again later',
    'Concentrate and ask again',
    'My reply is no',

print(messages[random.randint(0, len(messages) - 1)])
>>> name = 'Zophie'


>>> name[0]
'Z'
>>> name[-2]
'i'
>>> name[0:4]
'Zoph'
>>> 'Zo' in name
True
>>> 'z' in name
False
>>> 'p' not in name
False

>>> for i in name:
... print('* * * ' + i + ' * * *')

* * * Z * * *
* * * o * * *
* * * p * * *
* * * h * * *
* * * i * * *
* * * e * * *

2.2. Dictionary 

import pprint
import os

allGuests = {
    'Alice': {'apples': 5, 'pretzels': 12},
    'Bob': {'ham sandwiches': 3, 'apples': 2},
    'Carol': {'cups': 3, 'apple pies': 1}
}


def totalBrought(guests, item):

    numBrought = 0

    for k, v in guests.items():
         pprint.pprint(k)
         pprint.pprint(v)
        numBrought += v.get(item, 0)
    return numBrought


os.system("cls")

print('Number of things being brought:')
print(' - Apples ' + str(totalBrought(allGuests, 'apples')))
print(' - Cups ' + str(totalBrought(allGuests, 'cups')))
print(' - Cakes ' + str(totalBrought(allGuests, 'cakes')))
print(' - Ham Sandwiches ' + str(totalBrought(allGuests, 'ham sandwiches')))
print(' - Apple Pies ' + str(totalBrought(allGuests, 'apple pies')))
  • Result:
Number of things being brought:
- Apples 7
- Cups 3
- Cakes 0
- Ham Sandwiches 3
- Apple Pies 1

2.3. Tuple

The tuple data type is almost identical to the list data type, except in two ways. First, tuples are typed with parentheses, ( and ), instead of square brackets, [ and ]. For example, enter the following into the interactive shell:

>>> eggs = ('hello', 42, 0.5)
>>> eggs[0]
'hello'
>>> eggs[1:3]
(42, 0.5)
>>> len(eggs)
3

But the main way that tuples are different from lists is that tuples, like strings, are immutable. Tuples cannot have their values modified, appended, or removed. Enter the following into the interactive shell, and look at the TypeError error message:

>>> eggs = ('hello', 42, 0.5)
>>> eggs[1] = 99
Traceback (most recent call last):
File "<pyshell#5>", line 1, in <module>
eggs[1] = 99
TypeError: 'tuple' object does not support item assignment

2.4. Converting Types with the list() and tuple() Functions:

Just like how str(42) will return '42', the string representation of the integer 42, the functions list() and tuple() will return list and tuple versions of the values passed to them:

>>> tuple(['cat', 'dog', 5])
('cat', 'dog', 5)
>>> list(('cat', 'dog', 5))
['cat', 'dog', 5]
  • Important:
>>> list("This is a Program")
['T', 'h', 'i', 's', ' ', 'i', 's', ' ', 'a', ' ', 'P', 'r', 'o', 'g', 'r', 'a', 'm']

Converting a tuple to a list is handy if you need a mutable version of a tuple value.

3. Special Uses

3.1. Working with PDF and Word Documents

3.2. Working with CSV Files and JSON Data

3.3. Pattern Matching with Regular Expressions

3.4. Reading and Writing Files

3.5. Organizing Files

3.6. Web Scraping

3.7. Working with Excel Spreadsheets

4. Generalities

4.1. Importing Modules:

import random, sys, os, math

for i in range(5):
    print(random.randint(1, 10))

4.2. Ending a Program Early with the sys.exit() Function:

import sys

while True:
    print('Type exit to exit.')
    response = input()
    if response == 'exit':
        sys.exit()
    print('You typed ' + response + '.')

4.3. Handle Command Line Arguments

import sys

if len(sys.argv) < 2:
    print('Usage: python mclip.py [keyphrase] - copy phrase text')
    sys.exit()

keyphrase = sys.argv[1] # first command line arg is the keyphrase

Lambda Programming

from datetime import date
from functools import reduce


def numOfDays(date1, date2):
	return reduce(lambda x, y: (y-x).days, [date1, date2])


date1 = date(2018, 12, 13)
date2 = date(2019, 2, 25)
print(numOfDays(date1, date2), "days")

# This code is contributed by Jyothi pinjala

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