Python Cheat Sheet: The Basics
Python Data Types
List
In d ex ing
Accessin g data from a strin g , list, or tuple usin g an element number
Chan g eable collection of ob j ects
my_collection = [1, 1, 3.12, False, "Hi"]
String
my_tup [ element_number ]
List Operations
# returns the length of a lis t
Slicing
len(my_collection)
String Operations
Accessin g a subset of data from a strin g , list, or tuple usin g element numbers from start to stop -1
# returns the string with all uppercase letters
#
my_string.upper()
my_collection.extend( [ " M ore", " I tems" ] )
# returns the length of a string
#
Add multiple items to a list
len(my_string)
# returns the index of the first instance of the string inside the #
# subject string, otherwise -1
del(my_collection [ 2 ] )
# replaces any instance of the first string with the second in my_string
my_string.replace('H', 'C')
Delete the object of a list at a specified index
# Clone a lis t
clone = my_collection [:]
a == b
Less T han
["a", "b", "c"]
my_collection_3 = my_collection + my_collection_2
my_integer = 12321
# Calculate the sum of a list of ints or floats
number_collection =
[1,2,3,4.5]
Boolean
# Chec k if an item is in a list, returns
Boolean
in my_collection
# Chec k if an item is not in a list, returns B oolea n
item not in my_collection
item
Discrete value true or false
Dictionary
Chan g eable collection of key - value pairs
my_dictionary =
{'banana': 1, 12: 'laptop', (0,0):'center'}
Dictionary Operations
Access value using key
my_dictionary [ 'banana' ]
#
Get all keys in a dictionary as a list
my_dictionary. k eys()
#
Get all values in a dictionary as a list
my_dictionary. v alues()
a =
b =
Set Operations
# Con v ert a list to a se t
my_set = set( [ 1,1,2,3 ] )
# A dd an item to the se t
a.add( 4 )
tup = (1, 3.12,
False, "Hi")
Less T han or Eq ual
a
<= b
Not Equal
!= b
Con d itional Operators
# R emo v e an item from a se t
a.remo v e(" B ye")
Conditional O perators evaluate the operands and produce a true of false result
And - returns true if both statement a and b are true, otherwise false
b
a and b
# R eturns intersection of set a and
a.intersection(b)
# R eturns the union of set a and
a.union(b)
>= b
+: Additio
-: Subtractio
*: Multiplicatio
/: divisio
//: Integer Division (Result rounded to the nearest integer)
#
Tu ple
Unchangeable collection of objects
> b
Python Operators
{100, 3.12, False, "Bye"}
{100, 3.12, "Welcome"}
# R eturns set a minus
a.difference(b)
a
a
Set
Unordered collection of unique objects
a = True
b = False
< b
Greater Than
a
A decimal number
my_decimal = 3.14
a
Greater Than or Equal
sum(number_collection)
Float
Comparison O perators compare operands and return a result of true or false
Equal
my_collection_2 =
A whole number
my_collection [ start : stop ]
Co m parison Operators
# Concatenate two lists
Integer
my_string [ start : stop ]
my_tup [ start : stop ]
Add a single item to a list
my_collection.append(" S ingle")
my_string.find('l')
my_string [ element_number ]
my_collection [ element_number ]
Series of characters or data stored as text
my_string = "Hello"
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b
b
# R eturns T rue if a is a subset of b, false otherwis e
a.issubset(b)
# R eturns T rue if a is a superset of b, false otherwis e
a.issuperset(b)
Or - returns true if either statement a or b are true, otherwise false
a or b
Not - returns the opposite of the statement
not a
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Python Cheat Sheet: The Basics
Wor k ing w ith Files
Webscraping
Loops
For Loops
Reading a File
# Import BeautifulSoup
from bs4 import BeautifulSoup
for x in range(x):
# Executes loop x number of times
for x in iterable:
# Executes loop for each object in an iterable like a string, tuple,
list, or set
while statement:
# Executes the loop while statement is true
Conditional Statements
Opens a file in read mode
file = open(file_name, " r ")
# R eturns the file name
file . name
# R eturns the mode the file was opened i n
file . mode
#
# P arse HTML stored as a strin g
soup = B eautiful S oup(html, ' html 5 lib ' )
# R eturns formatted htm l
soup . prettif y ()
# F ind the first instance of an
soup . find(tag)
While Loops
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# F ind all instances of an
soup . find_all(tag)
HTML tag
Reads the contents of a file
file . read()
#
HTML tag
Re qu ests
Reads a certain number of characters of a file
file . read(characters)
#
Read a single line of a file
file . readline()
#
if statement_1:
# Execute of statement_1 is true
elif statement_2:
# Execute if statement_1 is false and statement_2 is true
else:
# Execute if all previous statements are false
Try/Except
# Import the re q uests librar y
import re q uests
#
#
to try to execute
to execute if there is an error of type a
to execute if there is an error of type b
to execute if there is any exception that has not been handled to execute if there is no exception
Get the url of the response
response . ur l
#
try:
# Code
except a:
# Code
except b:
# Code
except:
# Code
else:
# Code
Send a get requests to the url with optional parameters
= requests.get(url, parameters)
response
Get the status code of the response
Closes a file
file . close()
#
Writing to a File
response . status_code
#
Get the headers of the request
response . re q uest . header s
#
#
Opens a file in write mode
= open(file_name, "w")
file
Get the body of the requests
response . re q uest . bod y
Get the headers of the response
response . header s
# G et the content of the response in tex t
response . tex t
# G et the content of the response in j so n
response .j son ()
#
Error Types
Send a post requests to the url with optional parameters
re q uests . post(url, parameters)
#
IndexError - When an index is out of rang
Read all the lines of a file and stores it in a list
file . readlines()
#
#
Writes content to a file
file . write(content)
#
Adds content to the end of a file
file . append(content)
Objects and Classes
Creating a class
NameError - When a variable name is not foun
#
SyntaxError - When there is an error with how the code is written
class class_name:
ZeroDivisionError - When your code tries to divide by zero
Range
F u nctions
def __init__(self . optional_parameter_1, optional_parameter_2):
self . attribute_1
#
= optional_parameter_1
self . attribute_2 = optional_parameter_ 2
Create a function
def function_name(optional_parameter_1, optional_prameter_2):
def method_name(self, optional_parameter_1):
# code to execute
Produce an iterable sequence from 0 to stop-1
#
return optional_output
Code to execute
return optional_output
range(stop)
Produce an interable sequence from start to stop-1 incrementing by step
range(start, stop, step)
Calling a function
output = function_name(parameter_1, parameter_2)
#
Create an instance of a class
object = class_name(parameter_1, parameter_2)
#
# Callin g an ob j ect metho d
ob j ect . method_name ( parameter_ 3)
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