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Python Cheat Sheet by

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python

Vocabulary

variable
something that can change
string
a list of characters
integer number
pos/neg natural numbers and zero
floating point
decimal number
length
the length of the string
Modulo
Finds the remainder
Boolean
True/False
Syntax
Gramma­r/S­tru­cture of language
range (1,10)
the numbers 1-9
range(10)
the numbers 0-10

Condit­ionals

If..... :then..... else.......
If the statement is true then do command under then else do command under else
while......
While this is true loop the command under the condit­ional
While True
loops forever
for each item in name of list
For every item in the list repeat the command under the loop that many times. (a string is a list too)

Naming Conven­tions

Rules for naming variab­les:
- letters
- numbers
- unders­cores (_)
- can start with lett­ers or unde­rsc­ores ONLY
- NO SPACES

Valid names:
- _mystr
- my3
Hello_­there

Invalid names:
- 3my= "­hi" -- cannot start with number
- first name = "­hi" -- no spaces allowed
- first­-­name -- dashes are not accepted

Lists

#this is how you maek a list in python

shoppinglist = ['coke zero', 'bacon', 'water', 'jelly', 'gummy bears']

print (shoppinglist)

print (shoppinglist[0])
#prints the first item of the list

list_num = 0

while list_num < len(shoppinglist):
    print ("List:", shoppinglist[list_num])
    list_num =list_num+1
    

#for loop--> same as the above
    #For every item in that list we're going to print it.

for item in shoppinglist:
    print (item)



numbers = range(1,5)
#print up until less then the last number.
for item in numbers:
    print (item)

# a string is a list of characters, letters, numbers, etc.

mystr = "hello"

for letter in mystr:
    print (letter)

Adding strings number

mystring = ""
count = 0
while count < 5:
    mystring = mystring + str(count)
    print (mystring)
    count = count + 1
 

Symbols

==
equal to
!=
not equal to
<
less than
<=
less than or equal to
>
greater than
>=
greater than or equal to
+
add
-
subtract
*
multiply
/
divide and quotient is float
//
divide and quotient is integer
**
exponent
%
modulo: the remainder
[...]
The position of the item in the list or the letter in a word

Multip­lic­ation & Exponents

string * string
CRASH!!!
string * number
combines the strings multiple time
number * number
math (multiply)
string ** number
CRASH!!!
number ** number
Expone­nt(­Math)
string ** number
CRASH!!!

Even/odd using counters

even_value = 0
odd_value = 0
while True:
    user_input = input("Enter a positive number: ")
    number = int(user_input)
    if number < 0:
        print ("There were ", even_value ,"even numbers and there were " , odd_value ,"odd numbers.")
        break
    if number % 2 == 0:
        even_value = even_value + 1
    else:
        odd_value = odd_value +1

Addition

string + string
squishes them together
string + number
crash
number + number
math(a­ddi­tion)

Area of circle

def areaofCircle(r):
    if r <= 0:
        return "Error: invalid radius"
    
    pi = 3.1415
    area = pi(r*2)
    return (area)
user_radius = input('Enter the radius: ')
radius = float(user_radius)
print("The area of the circle is", areaofCircle(radius))

fibonacci

num1= 0
num2=1
mystr = '0'

while num1 + num2 < 89:
    Fibonacci = num1 +num2
    
    num1= num2
    
    num2=Fibonacci
    mystr= mystr+"," + str(num1)
print (mystr)

Functions

def calc(num1, num2, operation):
    
    if operation == "sum":
        return sum(num1, num2)

    elif operation == "product":
        return product(num1, num2)

    elif operation == "diff":
        return diff(num1, num2)

    elif operation == "div":
        return div(num1, num2)

    
def sum(a, b):
    return a+b

def product(a, b):
    return a*b

    
def diff (a, b):
    return a-b
    

    
def div(a, b):
    if b == 0:
        return ("Error")
    elif b != 0:
        return a/b
    

    

print (calc(1,2,"sum"))
print (calc(4,2, "diff"))
print (calc (9,0, "div"))
print (calc (2,12, "product"))

calc(1, 2, "sum")
 

Functions

print()
displays inform­ation on the screen
input()
receives info from the user
int()
converts the value into an integer
str()
converts the value to a string
float()
converts the value to a floating point
len()
The length of the string
#
One line comment not include in code
'''
Multi-line comment
def name(v­ari­able):
defines a block as in subbing the name for lines of commands. The variable in the parent­heses can be replaced by inputing the desire value into those parent­heses.
range (100)
range of numbers from 0 to one less then that.

Spelling a string out in reverse code

word = input("Type in an word: ")
reverse = ""
for letter in word:
    reverse = letter + reverse
print ("Reverse: ", reverse)

This prints the true or false value using boolean

print(True)
print (2<3)
print (2 != 2)

Countdown Code

user_number = input("Please enter a number: ")

number = int(user_number)

countdown_string = ""

while number > 0:
    countdown_string = countdown_string + " " + str(number)
    number = number-1

print (countdown_string)

palindrome and efficient loops


def isPalindrome(word):
    
    
    letter_num =0
    while letter_num < len(word)-1-letter_num:
        
        if word[letter_num] == word[len(word)-1-letter_num]:
            letter_num = letter_num +1
            
        else:
            return False
    return True
    
while True:
    user_input = input("Please type in a word: ")
    if user_input == "quit":
        break
    #print (isPalindrome(user_input))
    myvalue = isPalindrome(user_input)
    if myvalue == True:
        print (user_input + " is a palindrome.")
    elif myvalue == False:
        print (user_input + " is not a palindrome.")

list loops #2

word = input("Type in an word: ")
reverse = ""
for letter in word:
    reverse = letter + reverse
"""
letter_num = 0

reverse = ''

while letter_num < len(word):
    reverse = (word[letter_num] + reverse)
    letter_num = letter_num + 1
"""

    

print ("Reverse: ", reverse)

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