python3

last edited Wed, 24 Jul 2024 05:21:40 GMT
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Syntax Basics direct link to this section

operators direct link to this section

Exponent 2 ** 3 = 8 Modulus 22 % 8 = 6 Integer Division 22 // 8 = 2 Division 22 / 8 = 2.75 Multiplication 3 * 5 = 15 Subtraction 5 - 2 Addition 2 + 2

string concatenation direct link to this section

'alice' + 'bob' = 'alicebob'

• you can't concatenate integer values with string values without converting values

string replication direct link to this section

'alice' * 5* = 'alicealicealicealicealice'

comments direct link to this section

# this is a comment

essential functions direct link to this section

print('What is your name?') # ask for their name myName = input() stored as string according to user input

• may give errors with pytho n 2 as string not defined print(len(myName)) evaluates the integer value of the number of characters in a string >>> str(29) = '29' str() converts int to string, useful for concatenation int() convert string value to an integer spam = int(spam) note: an integer can be equal to a floating point

Flow Control direct link to this section

blocks are denoted by indentation **if-else **

if name == 'Alice': 
	print('Hi, Alice.') 
else: 
	print('Hello, stranger.')

• An else statement doesn’t have a condition
  • ensures one clause is executed

else if

• follows an if or elif statement
• provides another condition that is checked only if all of the previous conditions were False
  • order matters!

if name == 'Alice': 
	print('Hi, Alice.')
elif age < 12: 
	print('You are not Alice, kiddo.')

• the rest of the elif clauses are automatically skipped once a True condition has been found while loop

spam = 0 
while spam < 5: 
	print('Hello, world.') 
	spam = spam + 1

break keyword allows to break out of while clause early continue execution jumps to the start of the loop, re-evaluates condition for loop used with the range() function

print('My name is') 
for i in range(5): 
	print('Jimmy Five Times (' + str(i) + ')')

range() function The first argument is where the for loop's variable starts, the second will be up to the number to stop at.

for i in range(12, 16): 
	print(i)

In this example the third argument will be the step argument. The amount the variable increases by through each iteration.

for i in range(0, 10, 2):
	print(i)

range func accepts negative arguments to count down instead of up importing modules

import random, sys, os, math

Functions direct link to this section

defining a function

def hello(name):
	print('Hello, ' + name)
hello('Alice') 
hello('Bob')

Functions with Parameters

 def function_name(parameter: data_type) -> return_type:
    """Docstring"""
    # body of the function
    return expression

None keyword

• only NoneType data type
• useful since all function calls must evaluate to a return value
• Python adds return None to the end of any function definition with no return statement

global statement

• modify a global variable from within a function
• eggs refers to the global variable

def spam():
	global eggs
	eggs = 'spam'
eggs = 'global' 
spam() 
print(eggs)

exception handling

• program execution moves to the start of a following except clause if an error happens

def spam(divideBy):
	try: 
	return 42 / divideBy 
except ZeroDivisionError: 
	print('Error: Invalid argument.') 
print(spam(2)) 
print(spam(12)) 
print(spam(0)) 
print(spam(1))

Lists direct link to this section

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

for loops with lists

for i in [0, 1, 2, 3]:
	print(i)

in and not in Operators

>>> 'howdy' in ['hello', 'hi', 'howdy', 'heyas'] 
 True

tuple unpacking

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

Finding a Value in a List with the index() Method

>>> spam = ['hello', 'hi', 'howdy', 'heyas']
>>> spam.index('hello') 
0 
>>> spam.index('heyas') 
3

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

• append() adds new value to the end of a list

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

• the insert() method can insert a value at any index in the list
• the first argument is the index for the new value, and the second argument is the new value to be inserted

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

Removing Values from Lists with the remove() Method

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

Sorting the Values in a List with the sort() Method

you cannot sort lists that have both number values and string values in them

>>> spam = [2, 5, 3.14, 1, -7]
>>> spam.sort()
>>> spam
[-7, 1, 2, 3.14, 5]

• can sort values in reverse

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

• “ASCIIbetical order” rather than actual alphabetical order for sorting strings. This means uppercase letters come before lowercase letters

Reversing the Values in a List with the reverse() Method

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

The copy Module’s copy() and deepcopy() Functions direct link to this section

• If the list you need to copy contains lists, then use the copy.deepcopy() function instead of copy.copy(). The deepcopy() function will copy these inner lists as well

Dictionaries and Structuring Data direct link to this section

Manipulating Strings direct link to this section

Automating Tasks direct link to this section

Pattern Matching with Regular Expressions direct link to this section

regexes for short, are descriptions for a pattern of text

• you must import the packages to use regex functions

>>> import re

>>> phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')

matching regex objects

• use the search() method

Input Validation direct link to this section

Reading and Writing Files direct link to this section

Organizing Files direct link to this section

Debugging direct link to this section

Web Scraping direct link to this section

Essential modules:

• webbrowser comes with base install, opens browser to page(s)
• requests downloads files and web pages
• bs4 HTML parser
• selenium controls browser, can simulate mouse clicks

Working with Excel Spreadsheets direct link to this section

Working with Google Cheets direct link to this section

Working with PDF and Word Documents direct link to this section

Working with CSV Files and JSON Data direct link to this section

Keeping Time, Scheduling Tasks, and Launching Programs direct link to this section

Essential Modules:

• time
• datetime

time.time()

Unix Epoch returns the number of seconds since 12am January 1, 1970 as a float value.

time.ctime() returns a string description that's human readable

time.sleep()

Useful for having a program pause. Takes the time to stay idle in seconds as an argument.

round()

Rounds a float to the precision specified. Takes the number to be rounded as an argument. There is an optional second argument representing how many digits after the decimal to round to. If no second argument is passed then the number is rounded to the nearest whole integer by default.

Sending Email and Text Messages direct link to this section

Manipulating Images direct link to this section

Controlling the Keyboard and Mouse With GUI Automation direct link to this section

Libraries direct link to this section

References direct link to this section

Automate the Boring Stuff with Python