python.md

Python 3

"weakly typed" language

Variable type

Int=3, Float=3.0, String=”Words” (‘w’, “w”, “””w”””, ‘’’w’’’)

Accesing String

b = "Hello, World!"
print(b[2:5])
# llo

List (Mutable Type -> References point to same place)

# Declaring a new list , list can have a mixture of variables
x=[“ham”,4.22,5] 

# Accessing list
print(x[0]) #prints "ham"

# Checking if list is empty
if a==[]: 
  print “list is empty”
  
# Iterating through list
list = [1, 3, 5, 7, 9] 
for i in list: 
    print(i)
    
for i in range(6):
    print(i)
 #Print 0,1,2,3,4,5
  
##deep copying for deep arrays
list1=list2                       #list1 points to same reference as list2
list1=list2[:]                    #list1 points to a copy of list2, changes in list2 does not affect list1
from copy import deepcopy       # or import copy
list2=deepcopy(list1)         	#works for deep list

Starting : x=[“ham”,4.22,5]

Function	Description	Result
x.append(5)	#Add stuff into list	[“ham”,4.22,5,5]
x.insert(0,3.1)	#Insert stuff into the list	[3.1,“ham”,4.22,5]
x.pop(1)	#remove stuff from the list	[“ham” ,5]
len(x)	#number of items in list	len([“ham”,4.22,5]) returns 3
list(“ham”)	#converting string into list	[“h”,”a”,”m”]
in	Tree Insert	#check if item is in list
x[0],x[1]	#first item, second item	“ham”,4.22
x[1:3]	#slicing the list	[“4.22”,5] 2nd item to 4th item not including 4thitem
x[1:3:2]	#slicing increase increment	[“4.22”] increased increment to 2
x[::-1]	#reverse the list	[1,2,3]>>>[3,2,1]
x= [“c”]+x	#adding a list in front
x*2	#repeat 2 times	[“ham”,4.22,5,“ham”,4.22,5]
list.index(“ham”)	#returns the index of first found variable
list.sort()	#arrange from lowest to highest	[1, 2, 3, 4]

Tuple (Similar to List, use less memory and not adjustable)
(Immutable Type -> So their id(), the spot they point to in memory, changes.)

x=(“ham”,4.22,5)
x[1] #calling a tuple same as list

#Error
x[1]=3 #immutable cant be changed

Dictioanries: aka hashtables and maps
(Mutable Type)

# Declaring dictioanry
exDict={‘Jack’:[15,’blonde’],’Bob’:[22,’brown’]}
print(exDict[“Jack”][1])

#Accessing and adding new key,value
mydict = {"cat":12, "dog":6, "elephant":23}
mydict["mouse"] = mydict["cat"] + mydict["dog"]
print(mydict["mouse"]) # ans =6+12=18

#getting a list of keys()
dict1.keys()

Recursion

Base case (terminating), Recursion

# Complete the jumpingOnClouds function below.
def jumpingOnClouds(c):
    # inputs:  (list) c
    # outputs: (int) minNumJump
    # Recursion: 2 case 
    #   1) Jump 2 and succed  
    #   2) Jump 2 and fail / Jump 1 (reduce c_list)
    # Terminating case
    #   1) if there 1 jump left
    #   2) if there 2 jump left 
    
    jumps=0;
    jumpsLeft=len(c);
    #Termintating
    if(jumpsLeft==3 or jumpsLeft==2):
        #end
        jumps=1
        print("end jump")
        print(jumps)
        return jumps
        #add to jump and return
    else:
        #Recursion
        if(c[2]==0):
            #jump2 Success
            print("jump2")
            jumps=1
            jumps =jumpingOnClouds(c[2:len(c)])+jumps
            print(jumps)
            return jumps
        else:
            #jump1 
            print("jump1")
            jumps=1
            jumps =jumpingOnClouds(c[1:len(c)])+jumps
            print(jumps)
            return jumps