Tuesday, April 18, 2023

Ch 1 - Python's builtin functions

The most commonly used Python builtin function: print()

“print()” function displays the value of argument passed to it.
print(5): prints 5 
print(“hello world”): prints the message “hello world”

Some other built-ins that come in handy are: input(), len(), type() etc.
first_name = input(“Enter your first name: ”)
len(“Rakesh”) --> 6

len()

It tells you the number of characters in the string.

>>> len("rakesh")
6

>>> len("vikash")
6

It is also able to tell you the number of elements in a list / sequence.

>>> len([1, 2, 3, 5, 7])
5

>>> len(['rakesh', 'vikash', 'ashish'])
3

Some Numbers Related Builtin Functions

abs() Returns the absolute value of a number
bin() Returns the binary version of a number
complex() Returns a complex number
divmod() Returns the quotient and the remainder when argument1 is divided by argument2
max() Returns the largest item in an iterable
min() Returns the smallest item in an iterable
pow() Returns the value of x to the power of y
range() Returns a sequence of numbers, starting from 0 and increments by 1 (by default)
round() Rounds a number
sum() Sums the items of an iterator

Some Examples

Exaplanation of seeing 36 in binary form:

First: quotient

Second: remainder

Return the value of 4 to the power of 3 (same as 4 * 4 * 4):

Some more examples
>>> l = [5, 6, 2, 0, 9]
>>> max(l)
9
>>> min(l)
0
>>> sum(l)
22    

range()

Range takes three arguments: start, stop, step
But start and step are optional. What does that mean?
They can some default values, like:
Start: 0
Step: 1
Note: Range is exclusive of 'stop'

>>> list(range(1, 11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> 
>>> 
>>> list(range(2, 20, 2))
[2, 4, 6, 8, 10, 12, 14, 16, 18]
>>> 

>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> 
>>> 
>>> list(range(0, 10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> 
>>> list(range(0, 10, 2))
[0, 2, 4, 6, 8]
>>> 
>>> list(range(0, 10, 3))
[0, 3, 6, 9]
>>> 

pow()

>>> pow(2, 5)
32
>>> 2 ** 5
32

Python is very flexible. In most situations, it gives you more than one way to do things.

Some Type Casting Related Builtin Functions

bool() Returns the boolean value of the specified object
dict() Returns a dictionary (Array)
float() Returns a floating point number
int() Returns an integer number
list() Returns a list
set() Returns a new set object
str() Returns a string object
tuple() Returns a tuple (tuple is an immutable list)
type() Returns the type of an object

Type Casting Built-ins: bool()

>>> 0
0
>>> True
True
>>> bool(0)
False
>>> bool(-1)
True
>>> bool(1)
True
>>> 

Extra Information:
Q1: Trick question about a set.

>>> {True, False, True}
{False, True}
>>> {True, False, 0, 1}
{False, True}

Q2: Trick question about if-else:
var = 0

if(True):
    print("Got True")

if(var):
    print("In If")
else:
    print("In Else")


int() and list()

>>> int("5")
5
>>> int("5XYZ")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '5XYZ'

>>> age = input("Enter your age: ")
Enter your age: 20
>>> type(age)
<class 'str'>
 
>>> salary = int(input("Enter your salary: "))
Enter your salary: 5000
>>> type(salary)
<class 'int'>
 
>>> age
'20'
>>> salary
5000

Some Examples of Type Casting Related Builtin Functions

We saw this in code for building a calculator:
num1 = float(input("Enter the 1st num:"))
Use of list() when you want to reverse a list:

Finding volume of a cube

# Variable declaration. s is holding the side length.
s = input("Enter the side: ") # input() gives you a string
print(type(s))
s = float(s) # Type casting builtin for getting the float value of r
volume=pow (s,3) # Computation
print(volume)

Some Builtins For Processing a List

enumerate() Takes a collection (e.g. a tuple) and returns it as an enumerate object
filter() Use a filter function to exclude items in an iterable object
iter() Returns an iterator object
map() Returns the specified iterator with the specified function applied to each item
range() Returns a sequence of numbers, starting from 0 and increments by 1 (by default)
reversed() Returns a reversed iterator
sorted() Returns a sorted list
slice() Returns a slice object
zip() Returns an iterator, from two or more iterators

Some Examples of Builtins For Processing a List (Part 1)

>>> l = [5, 1, 9, 2, 4, 7] # Here, your list is a sequence of integers.
>>> max(l)
9
>>> min(l)
1
>>> sum(l)
28
>>> 
>>> sorted(l)
[1, 2, 4, 5, 7, 9]
>>> 
>>> l
[5, 1, 9, 2, 4, 7]
>>> 
>>> list(reversed(l))
[7, 4, 2, 9, 1, 5]
>>> 
>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> 
>>> l = ["alpha", "beta", "gamma", "delta", "epsilon"] # sequence of strings
>>> max(l)
'gamma'
>>> 
>>> ord('a')
97
>>> ord('b')
98
>>> ord('g')
103
>>> min(l)
'alpha'
>>> 
>>> sorted(l)
['alpha', 'beta', 'delta', 'epsilon', 'gamma']
>>> list(reversed(l))
['epsilon', 'delta', 'gamma', 'beta', 'alpha']
>>>