Python Cheat Sheet

Variable Declaration and Assignment

# --- variable declaration and assignment ---
 
myVar = 5 # simple, single variable assignment
 
myVar = myFunction() # variable assignment... assuming myFunction() returns a value
 
var1, var2, var3 = 1, 2, 3 # multiple variable assignment

Data Types

# --- Data Types --- myInteger = 12 # variable assigned an integer
 
myFloat = 12.0 # variable assigned a float
 
myString = "twelve" # variable assigned a string
 
mySecondString = '12' # variable assigned a string
 
myBoolean = False # variable assigned a Boolean
 
dataType = type(myFloat) # determines data type/class of object
 
convInt = int(myFloat) # converts float to an integer
 
convFloat = float(myInteger) # converts integer to a float
 
convString = str(myInteger) # converts integer to string
 
print(round(4.8)) # rounds a float value to the nearest whole number
 
print(var1) # print command

Arithmetic Operators

# --- arithmetic operators ---
 
print( 2 + 2 ) # addition
 
print( 2 - 2 ) # subtraction
 
print( 2 * 2 ) # multiplications
 
print( 2.1 / 2 ) # division, always results in float: 2.1 / 2 evaluates to 1.05
 
print( 2.1 // 2 ) # floor divisiion, gives the result of the last even division. Result will be a "mathematical integer" but whether it's a Python int or float depends on numbers used. 2.1 // 2 evaluates to the float 1.0, while 5 // 2 evaluates to int 2
 
print( 5 % 2 ) # modulo (integer remainder), 5 % 2 evaluates to 1 (that's the 1 left over to get to 5 after 2 went into 4 evenly... see how floor division and modulo pair so well... 5 // 2 = 2, 5 % 2 = 1)
 
print( 2 ** 2 ) # power of.. 2**2 evaluates to 4

Assignment/Reassignment Operators

# --- assignment/reassignment operators ---
 
myNumt = 10 # assignment
 
myNum += 5 # "add and"... adds to previous value
 
myNum -= 5 # "substract and"... subtract from previous value
 
myNum *= 5 # "multiply and"... multiply by previous value
 
myNum /= 5 # "divide and"... divide by previous value

Comparison Operators

# --- comparison operators ---
 
myNum = 4 print( myNum < 2 ) # less than
 
print( myNum > 2 ) # greater than
 
print( myNum <= 4 ) # less than or equal to
 
print( myNum >= 2 ) # greater than or equal to
 
print( myNum == 2 ) # equal to print( myNum != 2 ) # not equal to

String Operators

# --- string operations --- # view all string methods: https://docs.python.org/3/library/stdtypes.html# string-methods
 
myCourse = "introduction to programming in Python"
 
courseLength = len(myCourse) # length function
 
courseProper = myCourse.title() # capitalizes first letter of each word
 
confirmLower = myCourse.islower() # determines if the string consists of lowercase characters
 
statement = "I love Python. Working with Python is amazing because, hello, it's Python!"
 
countPython = statement.count('Python')
 
name = 'John Jacob Jingleheimer Schmidt'
 
name[0:4] # slice a string
 
username = "Connie"
 
code = "C859"
 
userMessage = "Welcome to {}, {}.".format(code, username)
 
print( userMessage )
 
myNewPhrase = "cowabunga dude"
 
mySplitPhraseList = myNewPhrase.split(" ") # split method, returns a list
 
print(mySplitPhraseList)

Functions with Input and Output

# --- function with both input and output ---
 
def areaOf(width,height):
 
# function that accepts two inputs
 
return width * height # function body outputs calculated area
 
myArea = areaOf(4,6) # function call provides two arguments and saves return value to a variable -- we can assign a value with this function because it RETURNS a value
 
print( myArea ) # displays myArea

`if` / `elif` / `else` Statements

# --- if / elif / else statements ---
 
age = 16
 
if age < 16: # condition will evaluate to either True or False
 
print('you are not old enough to drive') # if condition is True, execute this block
 
elif age >= 16 and age <= 18: # second condition will evaluate to either True or False
 
print('you may drive with adult supervision') # if second condition is True, execute this block
 
else:
 
print('you may drive a vehicle') # both earlier conditions are False, execute this block

Boolean Operations

# --- Boolean operations ---
 
# Boolean and operation will always be false unless both sides are true
 
bool01 = True and False # ... so it's False
 
x = 3
 
bool01a = (x == 3) and (x > 9) # False!
 
bool01b = (x == 3) and (x >2) # True!
 
bool02 = True or False # but that's True! OR combos are True when any single condition is True (pro tip: generally limit OR to joining 2 conditions -- any more than that and you're likely to have one evaluate True unexpectedly)
 
bool03 = not (True and False) # True... since (True and False) is False, so the not flips it to True

Lists

# # --- Lists ---
 
myNumbers = [1, 4.8, 7, 9.2, 3, 0] # creates list
 
print(myNumbers[3]) # prints the fourth number from the list
 
print(myNumbers[-1]) # prints the last element from the list
 
yourNumbers = myNumbers[1:3] # creates a new list (via a slice) with the second and third values from myNumbers
 
altNumbers = myNumbers[:3] # creates a new list (slice!) with 1st, 2nd, and 3rd values from myNumbers
 
newNumbers = myNumbers[3:] # creates a new list (sliced again!) with 4th, 5th, and 6th values from myNumbers
 
matchList = 9.2 in myNumbers # looks for a match and returns Boolean value... True here
 
noMatch = 9.3 not in myNumbers # ensures a match does not exist in list... also True here since list does not contain 9.3
 
listLength = len(myNumbers) # counts items in list
 
listMax = max(myNumbers) # returns greatest element of list
 
listMin = min(myNumbers) # returns smallest element of list
 
listSort = sorted(myNumbers) # returns copy of list ordered smallest to largest
 
listSortAgain = sorted(myNumbers, reverse=True) # returns copy of list ordered largest to smallest
 
listSum = sum(myNumbers) # returns total sum of list values
 
myNames = ['Jessica', 'Connie', 'Amy']
 
myNames.append('Grace') # new value is added to end of list
 
myNames.pop() # removes last item from the list
 
myNames.pop(1) # removes second item from the list
 
listJoined = ", ".join(myNames) # a string is used to join together values from list
 
print('Welcome aboard ' + listJoined)

Sets

# --- Sets ---
 
# note that sets aren't nearly as important to the OA as strings, lists, and dictionaries
 
idNums = set() # creates a new set, empty
 
idNums.add(12345) # adds value to set
 
idNums.add(12367) # adds second value to set
 
idNums.add(12367) # adds third value to set, but it is duplicate so it will not be added
 
idNums.discard(12345) # removes value from set, if found
 
set(myNumbers) # converts the list from line 91 above to a set
 
list(idNums) # converts the set from line 121 into a list

Loops

# --- For Loop ---
 
# a FOR loop is a natural fit for looping over a container item by item
 
cities = ['Albany', 'Chicago', 'Boulder', 'Tampa']
 
for city in cities: # performs commands for each item within list
 
print('Welcome to the city of ' + city) # or
 
# print('Welcome to the city of {}'.format(city)) # get to know str.format() or the similar f strings way of building larger strings... concatenation with + gets old fast
 
sum = 0
 
for num in range(1,5): # runs loop for numbers 1 through 4, as range is exclusive of the ending position
 
sum += num
 
# --- While Loop ---
 
# a WHILE loop is like an IF that repeats as long as its condition stays True
 
temp = 34
 
while temp >= 32: # while condition is True loop will iterate
 
print(temp) temp -= 1 # variable must change state, moving towards satisfying condition
 
print('it is freezing') # loop is done (note indentation is moved back left), so temp must be down below 32 now
 
startValue = 0
 
while startValue < 20:
 
startValue += 1
 
if startValue == 4: # if statement checks for a specific value
 
break # stops the flow of the while loop prematurely
 
print(startValue) # it's 4!

Dictionaries

# --- Dictionaries ---
 
studentGrades = { # dictionary is created
 
'Orfu': 83, # first entry is added with key of str 'Orfu' and value of int 83
 
'Bismark': 98,
 
'Igor': 72
 
} # end of dictionary
 
if 'Igor' in studentGrades: # in verifies if key is in dictionary
 
print('student is in course')
 
print( studentGrades.get('Bismark') ) # get method looks up value by key, or...
 
# print(studentGrades['Bismark'] ) # you can use the key as if it was an index (it's not, but the syntax is the same)
 
for student in studentGrades: # for loop iterates over each entry in dictionary
 
print('{}, you earned {} on the final exam'.format(student, studentGrades[student]))

Tuples

# --- Tuples ---
 
# tuples aren't as important as strings, lists, and dicts either
 
# think of a tuple as a row of data... it is IMMUTABLE because you shouldn't just change the order of columns of data
 
myPhone = (877, 435, 7948) # tuple is created with three sections of a phone number
 
print( 'Call WGU at {}-{}-{}'.format(myPhone[0], myPhone[1], myPhone[2]) )

Reading and Writing Files

# --- Reading and Writing Files ---
 
# older, simpler, but more cumbersome syntax for opening files...
 
f1 = open('/my_path/my_file.txt','r') # opens a file object for reading (read-mode is default)... you can now use IO/filestream methods like read() and readlines() on f1
 
f1 = open('/my_path/my_file.txt','w') # opens a file object for writing and deletes what is in the file previously
 
f1 = open('/my_path/my_file.txt','a') # opens a file object for appending (don't worry about append mode for OA, just read and write modes)
 
f1.read() # reads the data from file into a string
 
f1.write('hello, friend') # writes to file
 
f1.readlines() # returns a list of strings, with each line of the file as one string entry
 
f1.close() # closes file
 
# a better structure for opening files!
 
with open('/my_path/my_file.txt','r') as f: # opens a file, names if f (or whatever you like), performs operations and automatically closes file
 
my_lines = []
 
for line in f: # looping directly over the file is also OK
 
my_lines.append(line.strip()) # this does essentially the same as what f.readlines() would do, except usign the string strip() method here removes newline characters
 
# when you leave the with/open() block the file closes automatically

Modules & Python Standard Library

# --- Modules & Python Standard Library---
 
# The only modules I would focus on for the exam are math and csv
 
# math
 
import math # imports the math module
 
print('The factorial of 3 is: {}'.format(math.factorial(3)))
 
print('The largest integer less than or equal to 5.6 is: {}'.format(math.floor(5.6))) # 5
 
print('The smallest integer greater than or equal to 5.6 is: {}'.format(math.ceil(5.6))) # 6
 
print('3 to the 5th power is: {}'.format(math.pow(3, 5))) # 243.0
 
print('The math constant e to the power of 3 equals: {}'.format(math.exp(3))) # don't confuse math.exp() with math.pow()
 
print('The square root of 6 is: {}'.format(math.sqrt(6)))
 
# csv
 
# reading csv and tsv files without the csv module, using plain old IO/filestream methods, is fine...
# with open("filename.txt", "r") as f:
 
# # when reading, I grab contents and get out of the open block
# contents = f.read()
 
# whole file as one big string
# contents = f.readlines() # a list of line by line strings, WILL have "\n" at the end of each
 
# but using csv makes it a little easier...
 
import csv
 
# the reader() method is the only one I suggest knowing contents = list(csv.reader(f)) # csv.reader(f, delimiter="\t") for .tsv files... I like to recast the reader as a list. # does one more step for us... makes a list (since we recast it) of lists instead of the list of strings we get from readlines()
 
# [ # ['1', 'Flossie', 'Levey', 'flevey0@jimdo.com', '129.134.226.30'],
 
# ["2", "Bob"...],
 
# ...
 
# ] print(contents)

adam's notes

Table of Contents

Python Cheat Sheet

Variable Declaration and Assignment

Data Types

Arithmetic Operators

Assignment/Reassignment Operators

Comparison Operators

String Operators

Functions with Input and Output

`if` / `elif` / `else` Statements

Boolean Operations

Lists

Sets

Loops

Dictionaries

Tuples

Reading and Writing Files

Modules & Python Standard Library

Notes

Graph View

Backlinks

adam's notes

Table of Contents

Python Cheat Sheet

Variable Declaration and Assignment

Data Types

Arithmetic Operators

Assignment/Reassignment Operators

Comparison Operators

String Operators

Functions with Input and Output

if / elif / else Statements

Boolean Operations

Lists

Sets

Loops

Dictionaries

Tuples

Reading and Writing Files

Modules & Python Standard Library

Notes

Graph View

Backlinks

`if` / `elif` / `else` Statements