Python Foundation Training Day 1

by Vikrant Patil

at MIT Pune, IT Dept. Mar 12-16, 2018

Notes are available online at

https://notes.pipal.in/2018/mit-pune-march/

print("Hello World!")

Hello World!

name = input()

python

print(name)

python

Basic data types

There are integers

1 + 2

3

2 -3

-1

2 *3

6

4/2

2.0

5//2

2

2 ** 3

8

2 ** 100

1267650600228229401496703205376

2 ** 1000

10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

5 % 2

1

There are floats

2.3 + 3.4

5.699999999999999

There are strings

name = "Rupali"

print(name)

Rupali

single = 'a string " quote inside it'

print(single)

a string " quote inside it

doublequotes = "a string with ' inside it"

print(doublequotes)

a string with ' inside it

name

'Rupali'

surname = "Rupak"

name + surname

'RupaliRupak'

x = "Rupali" "Rupak"

x

'RupaliRupak'

star = "*"

star*5

'*****'

"="*20

'===================='

multiline = """
this is
multi line string 
with few 
lines in
it
"""

print(multiline)

this is
multi line string 
with few 
lines in
it

s = "sdkjfhsdkjfhdskhjgf sdjgsad dkjhfds gkjhdsfgkjhadfg ksdjhgfkjdshg kjdfhg dfkjghdfgkjdsfh g dfkghdfkjgh dsfkhkgjdsfh "

s

'sdkjfhsdkjfhdskhjgf sdjgsad dkjhfds gkjhdsfgkjhadfg ksdjhgfkjdshg kjdfhg dfkjghdfgkjdsfh g dfkghdfkjgh dsfkhkgjdsfh '

print(multiline)

this is
multi line string 
with few 
lines in
it

multiline

'\nthis is\nmulti line string \nwith few \nlines in\nit\n'

twolines = "one\ntwo\t2"

print(twolines)

one
two	2

name1 = "Rupali Rupak"

name1

'Rupali Rupak'

"""one
two
three"""

'one\ntwo\nthree'

unicode = "\u0c85"

print(unicode)

ಅ

regional = "आ ड ब"

regional

'आ ड ब'

empty = ""

print(empty)

empty

''

There are binary arrays

binary = b"This is binary string"

binary

b'This is binary string'

binary1 = "\x056"

binary1

'\x056'

There are higher level data types.. Lists

digits = [0,1,2,3,4,5,6,7,8,9]

print(digits)

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

digits[0]

0

digits[-1]

9

digits[1:] # drop first

[1, 2, 3, 4, 5, 6, 7, 8, 9]

digits[3:] #drop first 3

[3, 4, 5, 6, 7, 8, 9]

digits[:3] # take first three

[0, 1, 2]

ones = [1,1,1,1]

ones + ones

[1, 1, 1, 1, 1, 1, 1, 1]

firstthree = digits[:3]

firstthree

[0, 1, 2]

digits

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

ones

[1, 1, 1, 1]

ones + ones

[1, 1, 1, 1, 1, 1, 1, 1]

ones * 5

[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

ones - ones

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-71-dd003c98adda> in <module>()
----> 1 ones - ones

TypeError: unsupported operand type(s) for -: 'list' and 'list'

ones * 1.2

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-72-50c18fd420ad> in <module>()
----> 1 ones * 1.2

TypeError: can't multiply sequence by non-int of type 'float'

ones - 1

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-73-80d12b1d54e4> in <module>()
----> 1 ones - 1

TypeError: unsupported operand type(s) for -: 'list' and 'int'

mixed = ["ones", "two", 1, 2, 3]

mixed

['ones', 'two', 1, 2, 3]

m = [[1,2,3],[4,5,6],[7,8,9]]

m[0] # 0th row

[1, 2, 3]

m[-1] # last row

[7, 8, 9]

m[0][2] #2nd element from 0th row

3

ones 

[1, 1, 1, 1]

ones[0]

1

ones[0] = 0

ones

[0, 1, 1, 1]

ones[0] = 1

tuples .. sibling of lists

t = (0,1,2,3,4)

t + t

(0, 1, 2, 3, 4, 0, 1, 2, 3, 4)

t * 4

(0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4)

t[0]

0

t[-1]

4

t[2:]

(2, 3, 4)

t[0] = 1

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-95-0a69537257d5> in <module>()
----> 1 t[0] = 1

TypeError: 'tuple' object does not support item assignment

origin = (0,0)

origin[0] = 2

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-97-415448be37c7> in <module>()
----> 1 origin[0] = 2

TypeError: 'tuple' object does not support item assignment

Dictionaries

person = {"name":"alice", "email":"alice@wonder.land", 
          "place":"wonmderland", "PIN":42}

person

{'PIN': 42,
 'email': 'alice@wonder.land',
 'name': 'alice',
 'place': 'wonmderland'}

person["name"]

'alice'

person["place"]

'wonmderland'

person['email']

'alice@wonder.land'

person

{'PIN': 42,
 'email': 'alice@wonder.land',
 'name': 'alice',
 'place': 'wonmderland'}

person["PIN"]

42

d = {"integer":2,
    "list":[1,2,3,4],
    "tuple":(1,2,3),
    2:"two"}

d

{'integer': 2, 'list': [1, 2, 3, 4], 'tuple': (1, 2, 3), 2: 'two'}

person['PIN'],person['email']

(42, 'alice@wonder.land')

x,y = 2,3

There are sets

s = {1,2,3}

sentence = """This is a randome statement from which we
will find out which english alphabets are used in this!"""

alphabets = set(sentence)

alphabets

{'\n',
 ' ',
 '!',
 'T',
 'a',
 'b',
 'c',
 'd',
 'e',
 'f',
 'g',
 'h',
 'i',
 'l',
 'm',
 'n',
 'o',
 'p',
 'r',
 's',
 't',
 'u',
 'w'}

What will be output?

s = "first second \nthird"

print(s)

first second 
third

s

'first second \nthird'

pre = "Isac"
post = "Asimove"

pre post

  File "<ipython-input-113-9f3396fba351>", line 1
    pre post
           ^
SyntaxError: invalid syntax

"Isac" "Asimove"

'IsacAsimove'

{"key":{"one":1}}

{'key': {'one': 1}}

Functions

len("what is length of this string")

29

len([1,2,3,4,5])

5

len((0,1,2,3,4))

5

len(person)

4

len(alphabets)

23

int("43")

43

int("A")

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-129-2e0b20450aad> in <module>()
----> 1 int("A")

ValueError: invalid literal for int() with base 10: 'A'

str(43)

'43'

list((1,2,3,4))

[1, 2, 3, 4]

t = (1,2,3,4)

l = list(t)

l

[1, 2, 3, 4]

t

(1, 2, 3, 4)

range(10)

range(0, 10)

list(range(10))

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

#list(range(100))

sum([1,2,3])

6

sum(["one", "two", "three"])

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-141-40a4ca8389f8> in <module>()
----> 1 sum(["one", "two", "three"])

TypeError: unsupported operand type(s) for +: 'int' and 'str'

help(sum)

Help on built-in function sum in module builtins:

sum(iterable, start=0, /)
    Return the sum of a 'start' value (default: 0) plus an iterable of numbers
    
    When the iterable is empty, return the start value.
    This function is intended specifically for use with numeric values and may
    reject non-numeric types.

sum(["one", "two", "three"])

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-144-83f2b8125102> in <module>()
----> 1 sum(["one", "two", "three"], "")

TypeError: sum() can't sum strings [use ''.join(seq) instead]

sum((1,2,3,4,5))

15

problems

find number of digits in 2^1000

2**1000

10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

n = 2**1000

n

10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

digits = str(n)

digits

'10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376'

len(digits)

302

2 ** 100

1267650600228229401496703205376

x = 2**100

Custom function

def add(x, y):
    s = x + y
    return s

def dummy():
    pass

def do_nothing():
    print("Print nothing")
    s = 2 +3
    
def twice(x):
    return 2*x

add(2,3)

5

dummy()

twice(3)

6

do_nothing()

Print nothing

problem

• Write a function count_digits which counts number of digits from given number
• Write a function sum_natural to find sum of first n natural numbers

def twice(x):
    return 2*x

def twice1(x):
    print(2*x)
    

What will be output of

print(twice(twice(3)))

What will be output of

print(twice1(twice1(4)))

a = add(2,3)

print(a)

5

def dummy():
    pass

r = dummy()

print(r)

None

r

def twice(x):
    return 2*x

def twice1(x):
    print(2*x)
    

twice(3)

6

twice1(4)

8

t = twice(3)

print(t)

6

t1 = twice1(4)

8

t1

print(t1)

None

More about functions

x = 2

x

2

def fun(x):
    return 3*x

fun

<function __main__.fun>

print(x)

2

print(fun)

<function fun at 0x7f19b84cfd08>

y = x

print(y)

2

aliasfun = fun

print(aliasfun)

<function fun at 0x7f19b84cfd08>

print(fun)

<function fun at 0x7f19b84cfd08>

fun(3)

9

aliasfun(4)

12

def sqaure(x):
    return x*x

def sumofsquares(x,y):
    return sqaure(x) + sqaure(y)

def cube(x):
    return x*x*x

def sumofcubes(x,y):
    return cube(x) + cube(y)

def sumof(f, x , y):
    return f(x) + f(y)

sumofsquares(2,3)

13

sumof(sqaure, 2, 3)

13

sumofcubes(2,3)

35

sumof(cube, 2, 3)

35

def make_adder(x):
    def adder(y):
        return x+y
    
    return adder

adder5 = make_adder(5)

adder5

<function __main__.make_adder.<locals>.adder>

type(adder5)

function

adder5(6)

11

adder5(7)

12

adder4 = make_adder(4)

adder4(5)

9

sum3 = lambda x,y,z : x+y+z

sum3(2,3,4)

9

problem

• Using lambda expression write above function make_adder

def make_adder(x):
    return lambda y: x+y

max([3,4,51,2,3,4])

51

max(["one","two","three","four","five"])

'two'

words = ["one","two","three","four","five"]

max(words)

'two'

max(words, key=len)

'three'

records = [
    ("A", 7.8),
    ("B", 8.7),
    ("C", 7.0),
    ("D", 5.5),
    ("E", 7.7)
]

records

[('A', 7.8), ('B', 8.7), ('C', 7.0), ('D', 5.5), ('E', 7.7)]

max(records)

('E', 7.7)

def get_score(t):
    return t[1]

max(records, key=get_score)

('B', 8.7)

min(records)

('A', 7.8)

min(records, key=get_score)

('D', 5.5)

sorted(records, key=get_score)

[('D', 5.5), ('C', 7.0), ('E', 7.7), ('A', 7.8), ('B', 8.7)]

sorted(words, key=len)

['one', 'two', 'four', 'five', 'three']

sorted(words)

['five', 'four', 'one', 'three', 'two']

sorted(records, key=lambda r:r[1])

[('D', 5.5), ('C', 7.0), ('E', 7.7), ('A', 7.8), ('B', 8.7)]

Methods from objects

Strings

s = "Some random statement"

s.lower()

'some random statement'

s.upper()

'SOME RANDOM STATEMENT'

s.count("e")

3

s.split(" ")

['Some', 'random', 'statement']

s.split()

['Some', 'random', 'statement']

words 

['one', 'two', 'three', 'four', 'five']

"_".join(words)

'one_two_three_four_five'

"/".join(["","home","vikrant", "trainings","2018"])

'/home/vikrant/trainings/2018'

" ".join(words)

'one two three four five'

trailingspces = "   jdkslfd kjdhsfkjhsd kjhfsdkfh      "

trailingspces.strip()

'jdkslfd kjdhsfkjhsd kjhfsdkfh'

"Wizard of oz was lisp".replace("lisp", "python")

'Wizard of oz was python'

filename = "hello.py"

filename.startswith("hello")

True

filename.endswith(".py")

True

s.center(50)

'              Some random statement               '

s.rjust(50)

'                             Some random statement'

s.ljust(50)

'Some random statement                             '

Lists

numbers = list(range(10))

numbers

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers.count(0)

1

ones.count(1)

4

ones

[1, 1, 1, 1]

numbers.append(10)

numbers

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.pop()

10

numbers

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers.pop(0)

0

numbers

[1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers.insert(0, -1)

numbers

[-1, 1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers.pop()

9

numbers.pop(0)

-1

numbers

[1, 2, 3, 4, 5, 6, 7, 8]

numbers.sort()

numbers

[1, 2, 3, 4, 5, 6, 7, 8]

numbers.sort(reverse=True)

numbers

[8, 7, 6, 5, 4, 3, 2, 1]

numbers.reverse()

numbers

[1, 2, 3, 4, 5, 6, 7, 8]

words

['one', 'two', 'three', 'four', 'five']

words.sort(key=len)

words

['one', 'two', 'four', 'five', 'three']

sorted(words, key=len, reverse=True)

['three', 'four', 'five', 'one', 'two']

words.extend(["six", "seven"])

words

['one', 'two', 'four', 'five', 'three', 'six', 'seven']

problem

• Write a function count_zeros which counts number of zeros in given number

  >>> count_zeros(1000)
  3

• Write a function head which returns first n elements from a list

  >>> head([1,2,3,4,5,6,7,8,9], 4)
  [1,2,3,4]

• Write a function rearrangemax which rearranges digits of given number to form a max number out of it.

  >>> rearrangemax(5498)
  9854

sum = 6

sum([1,2,3])

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-271-748a1806f572> in <module>()
----> 1 sum([1,2,3])

TypeError: 'int' object is not callable

del sum

sorted("hello world")

[' ', 'd', 'e', 'h', 'l', 'l', 'l', 'o', 'o', 'r', 'w']

def count_zeros(n):
    return str(n).count("0")

def head(items, n):
    return items[:n]

def rearrangemax(n):
    strn = str(n)
    orderd = sorted(strn, reverse=True)
    return int("".join(orderd))

count_zeros(10002)

3

head([1,2,3,4,5,6,7], 3)

[1, 2, 3]

rearrangemax(5678)

8765

filename

'hello.py'

i = filename.index(".")

filename[i+1:]

'py'

filename.split(".")

['hello', 'py']

filename.split(".")[-1]

'py'

tuples

t = (1,1,1,1,0,0,0)

t.count(1)

4

t.index(0)

4

t.append(0)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-292-78592bf72d62> in <module>()
----> 1 t.append(0)

AttributeError: 'tuple' object has no attribute 'append'

t.sort()

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-293-0708f4171c7e> in <module>()
----> 1 t.sort()

AttributeError: 'tuple' object has no attribute 'sort'

modules

import os

os

<module 'os' from '/home/vikrant/usr/local/anaconda3/lib/python3.6/os.py'>

type(os)

module

os.getcwd()

'/home/vikrant/trainings/2018/mit-pune-march'

os.listdir(os.getcwd())

['.ipynb_checkpoints', 'day1.ipynb']

os.listdir("/home/")

['mohini', 'lost+found', 'vikrant']

import math

math.pi

3.141592653589793

math.sin(math.pi)

1.2246467991473532e-16

from math import cos

cos(3.14)

-0.9999987317275395

import math as m

m.pi

3.141592653589793

m.sin(m.pi)

1.2246467991473532e-16

del math

math

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-311-674f3def7873> in <module>()
----> 1 math

NameError: name 'math' is not defined

m

<module 'math' from '/home/vikrant/usr/local/anaconda3/lib/python3.6/lib-dynload/math.cpython-36m-x86_64-linux-gnu.so'>

m.pi

3.141592653589793

cos

<function math.cos>

from math import sin

sin(3.14)

0.0015926529164868282

math

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-317-674f3def7873> in <module>()
----> 1 math

NameError: name 'math' is not defined

os.path.exists("/home")

True

os.path.getsize("day1.ipynb")

94690

os.listdir(os.getcwd())

['.ipynb_checkpoints', 'day1.ipynb']

def count_files(path):
    return len(os.listdir(path))

count_files("/home/vikrant")

63

count_files(".")

2

os.mkdir("/tmp/xyz")

os.path.exists("/tmp/xyz")

True

os.path.exists("/tmp/xyz1")

False

True

True

False

False

problem

• write a function biggestfile to find file with largest size from given directory

import os
def biggestfile(path):
    files = os.listdir(path)
    return max(files, key=os.path.getsize)

biggestfile(".")

'day1.ipynb'

Custom modules

%%file module.py
x = 42

def square(x):
    return x*x

def mean(x,y):
    return  (x+y)/2

def add(x,y):
    return x+y


def say_hello(name):
    print("Hello ", name)

Writing module.py

import module

module.x

42

module.square(43)

1849

module.say_hello("python!")

Hello  python!

%%file module1.py
import sys

def say_hello(name):
    print("Hello ", name)
    
print(sys.argv)

Overwriting module1.py

!python module1.py MIT

['module1.py', 'MIT']

!python module1.py MIT ITDEPT PUNE

['module1.py', 'MIT', 'ITDEPT', 'PUNE']

%%file hello.py
import sys


def say_hello(name):
    print("Hello ", name)
    
say_hello(sys.argv[1])

Writing hello.py

!python hello.py MIT

Hello  MIT