Types
str 
'abcd' 
int 
1,2,3,4 
float 
1.23 
bool 
True/False 
None 
None 
type('abc') 
shows the type of the object 
type conversion 
int('123') > 123 
bool(x) 
False for x values that are null or empty x. True for otherwise 
Naming conventions 
lowercase and underscore (_HAPPYday, happyday) 
Order of growth
def factorial(n): if n < 2: return 1 return n * factorial(n  1) 
O(n) 
def fib(n): if n < 2: return 1 return fib(n  1) + fib(n  2) 
O(2^n) (each branch produces another 2 branches) 
def foo(n): while n > 1: print(n) n = n // 2 
O(log n) 
def bar(n): while n > 1: x = n while x > 1: print(n, x) x = 1 n = 1 
O(n^2) (loop in a loop) 
def baz(n): while n > 1: x = n while x > 1: print(n, x) x = x // 2 n = 1 
O(n log n) (log n in a loop) 
String and tuple slicing 
Slicing is an O(n) operation as you need to create another string/tuple when you slice. 
def count_me(n): if n < 10: return n else: return count_me(n + 1) 
O(infinity) 
String and tuple concatenation 
O(n) 
Time complexity> looking at the branches of the tree
Space complexity> looking at the depth of the tree (depends on the pending operations the function incurred)
And also for analysing OOG questions:
for <loop>:
<do work>
Time
= work(1) + work(2)+...+work(n)
If work is fixed (let's say work = k) regardless of n, Time = n * k
Otherwise,
Time = sum of work
Remember to state what the n means
Recursive and Iteration
Recursion
def recusive_fn(n):
if <base case>:
return <base case value>
else:
return <manipulate recursive_fn(n1) such that it becomes nth case>
Iteration (for or while loop)
def iterative_fn(n):
temp = <some basic value>
for i in <range>:
<update temp>
return temp
def factorial (n):
product , counter = 1,1
while counter <= n:
product *= counter
counter += 1
return product

Tuples comparison
Tuples are compared position by position: the first item of the first tuple is compared to the first item of the second tuple (same as string); if they are not equal (i.e. the first is greater or smaller than the second) then that's the result of the comparison, else the second item is considered, then the third and so on.



Truth values revisited
Truth and False will be represented by 1 and 0 respectively.
not 'abc' > False
1 or 0 > 0
'' is same as False is same as 0 is same as []
while True: infinite looping
while False: will not loop at all

String and tuple slicing
s[start:stop(noninclusive):step]
eg) s = "12345", d ='6789'
concatenate> s + d> '123456789'
s[0] = "1", s[1:]= "2345", s[:2]= "12", s[1:5:2] = "13"
s[1] = "5", s[1:3] = "", s[3:1]= '34', s[5:1:2]= '13', s[5:1:2]= ''', s[1:5:2] = '53'

Variable (Global and Local)
Variable is local if assigned to in function
Namespaces match function and variable names to their definitions and assignments
Random module
random.randint(a, b) 
Return a random integer N such that a <= N <= b. 
random.randrange(start, stop[, step]) 
Return a randomly selected element from range(start, stop, step). This is equivalent to choice(range(start, stop, step)), but doesn’t actually build a range object 
random.random() 
Return the next random floating point number in the range [0.0, 1.0). 
random.random() can be scaled 
int(random.random() * 9999) → 3658 
break
for val in "string":
if val == "i":
break
print(val)
print("The end")
Output:
s
t
r
The end

The break statement terminates the loop containing it. Control of the program flows to the statement immediately after the body of the loop.
If break statement is inside a nested loop (loop inside another loop), break will terminate the innermost loop.
Hiding 'something'
Input an empty (lambda : "Prof is really cool")
In that way what is printed or sliced/accessed will be the function itself.
To recover the secret message, can input () at the back.



Functions
def <name>(formal parameters):
body
return (something if not it is going to return to zero)
Anonymous function→ lambda
lambda x: x+ 1
A function need not use every parameter passed into it. (def foo(a, b): return a + a)
A function without any parameters or return value is still valid. (def foo():return )
Functions do not necessarily need a return value.(def foo(a, b, c):a + b + c)

Conditionals
if <statement>:
do something
elif <statement>:
do something
else <statement>:
do something
while <statement>:
do something

Equality/ in function
is 
This means the same object. (3 is 3)> True 
== 
This mean the same content. (3.00 == 3) > True 
in 
check the elements inside the other group. Eg) x = (1,2,3). 1 in x> True 
Different Types of Error
NameError 
Raised when a variable is not found in local or global scope. 
IndexError 
Raised when index of a sequence is out of range. 
RuntimeError 
Raised when an error does not fall under any other category. 
SyntaxError 
Raised by parser when syntax error is encountered 
ZeroDivisionError 
Raised when second operand of division or modulo operation is zero. 
UnboundLocalError 
Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable 
RecursionError 
Infinite looping 
Tuple and string functions
len() 
Return the length (the number of items) in the tuple. 
max() 
Return the largest item in the tuple. 
min() 
Return the smallest item in the tuple 
sum() 
Retrun the sum of all elements in the tuple. 
tuple() 
Convert an iterable (list, string, set, dictionary) to a tuple. 
count() 
count the occurrences of an element in a tuple 
index() 
Searches the string for a specified value and returns the position of where it was found 
continue
for val in "string":
if val == "i":
continue
print(val)
print("The end")
Output:
s
t
r
n
g
The end

The continue statement is used to skip the rest of the code inside a loop for the current iteration only. Loop does not terminate but continues on with the next iteration.

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