Python Training at Arcesium - Day 1¶

Oct 25-27, 2017 Vikrant Patil

These notes are available online at http://notes.pipal.in/2017/arcesium-oct-python/day1.html

2 + 3

5

x = 3

x

3

x

3

print(x)

3

name = "Krishna"

print(name)

Krishna

raga = input()

asawary

print(raga)

asawary

print("Hello", name)

Hello Krishna

Basic data types¶

There are integers

2 + 2

4

2 * 2

4

2 - 4

-2

2 ** 5

32

8 % 2

0

2 ** 1000 # integers can be big!

10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

5 / 2

2.5

5 // 2

2

Python has floats

0.0001 + 1

1.0001

Python has string

first = "Rupali"

second = "Rupak"

print(first, second)

Rupali Rupak

name = first + " " + second

print(name)

Rupali Rupak

name = "Rupali" "Rupak"

name

'RupaliRupak'

five = str(5)

print(five)

5

five

'5'

star = "*"

rating = star *5

rating

'*****'

print("="*30)

==============================

twolines = "first\nsecond\nthird"

print(twolines)

first
second
third

multiline = """
first
second
third
"""

print(multiline)

first
second
third

s = "what's your name?"

print(s)

what's your name?

singlequote = 'in this string i can put double "'

print(singlequote)

in this string i can put double "

multi = '''
multiline
with 
signle quote
'''

print(multi)

multiline
with 
signle quote

regional = "आ ष"

print(regional)

आ ष

print("\u0c85\u0c86")

ಅಆ

Python has binary data reprersentation as bytes

binary = b'binary'

print(binary)

b'binary'

hex(ord("b"))

'0x62'

binary  = b'\x62\x69\x6e\x61\x72\x79'

print(binary)

b'binary'

There are special high level data types like list

letters = ['x','y','z']

letters[0]

'x'

letters[1]

'y'

letters[2]

'z'

len(letters)

3

ones = [1, 1, 1, 1]

moreones = ones + ones

moreones

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

stillmoreones = ones * 5

stillmoreones

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

mixedtypes = ["one", "two", 1, 2]

mixedtypes

['one', 'two', 1, 2]

mixedtypes[0] = "zero"

mixedtypes

['zero', 'two', 1, 2]

List has special mechanism to index various items

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

topten[-1]

9

topten[-2]

8

print(topten)

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

topten[:2]  #take first two elements

[0, 1]

topten[2:] # drop first two elements

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

head = topten[:2]

print(head)

[0, 1]

tail = topten[2:]

print(tail)

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

tail

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

topten

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

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

matrix[0] # 0th row

[1, 2, 3]

matrix[1] # 1st row

[4, 5, 6]

matrix[0][-1] # last element in 0th row

3

matrix[-1]

[7, 8, 9]

matrix[0] = [7,8,9]

matrix

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

There is another datatype similar to lists...called tuple ..

point = (1.1, 2.0)

print(point)

(1.1, 2.0)

triangle = ((0,0), (0,1), (1,1))

triangle[0] = (0,0.5)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-103-8608e9339ebf> in <module>()
----> 1 triangle[0] = (0,0.5)

TypeError: 'tuple' object does not support item assignment

ones = (1,1,1)

ones*5

(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)

ones + ones

(1, 1, 1, 1, 1, 1)

manyobjects = ((1,1,1), "one", ('a','b','c'))

t = (1,2,3, (1,1,1), [0,0,0])

t[2]

3

t[4]

[0, 0, 0]

t[4] = [3,4,5]

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-111-a8406b5489df> in <module>()
----> 1 t[4] = [3,4,5]

TypeError: 'tuple' object does not support item assignment

t[4][0] = 1

t

(1, 2, 3, (1, 1, 1), [1, 0, 0])

t[:2]

(1, 2)

t[2:]

(3, (1, 1, 1), [1, 0, 0])

t[-1]

[1, 0, 0]

Dictionary is named collection of objects

data = {"one":1, "two":2, "three":3}

data["one"]

1

machine = {"name":"mozart", "os":"mint", "brand":"acer"}

machine['name']

'mozart'

machine['os']

'mint'

d = {"names":["alice", "alex","david"]}

d['names']

['alice', 'alex', 'david']

Set

paragraph = """
1 some random text
2 to see how many english aphabets 
3 are being used while writing this
4 if I have some numbers in it 
"""

set(paragraph)

{'\n',
 ' ',
 '1',
 '2',
 '3',
 '4',
 'I',
 'a',
 'b',
 'd',
 'e',
 'f',
 'g',
 'h',
 'i',
 'l',
 'm',
 'n',
 'o',
 'p',
 'r',
 's',
 't',
 'u',
 'v',
 'w',
 'x',
 'y'}

set([1,2,1,1,2,3])

{1, 2, 3}

And of course there are booleans

sure  = True
arrr = False

print(sure, arrr)

True False

There is one more type for nothing

nothing = None

print(nothing)

None

Do it yourself¶

What is the difference in output of interpreter and output of print function for following case?
```
s = "Just to make sure , \nthat you understand new line"
s
print(s)
```

will this work?

pre  = "Isac"
post = "Asimov"
name = pre post

p = "Isac"
post = "Asimove"
together = p post

  File "<ipython-input-142-f04b22fac1c7>", line 3
    together = p post
                    ^
SyntaxError: invalid syntax

print(name)

RupaliRupak

s = "some value\n another value"

s

'some value\n another value'

print(s)

some value
 another value

Functions¶

len("Python")

6

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

5

len((1,2,3,4,5,56))

6

len({"jan":31, "feb":28,"Mar":31})

3

4 + int("2")

6

str(4) + "2"

'42'

Problem Using the function we know as of now, find number of digits in a given number. lets say 2 ** 100

digits = str(2**100)

digits

'1267650600228229401496703205376'

len(digits)

31

Custom functions¶

def square(x):
    v = x *x
    return v

print(square(4))

16

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

say_hello("Python")

hello Python

value = square(5)

print(value)

25

value = say_hello("Hari")

hello Hari

print(value)

None

Do it yourself

Write a function count_digits to count number of digits in given number. it should work as given below
```
>>> count_digits(2*100)
31
```

Before trying following code in interpreter , guess what will be output?

def twice(x):
    return 2*x

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

twice(twice(3))
twice1(twice1(3))

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

def twice(x):
    return 2*x

v = twice(3)

v

6

v1 = twice1(3)

6

print(v1)

None

twice1(None)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-166-d7c6acf71719> in <module>()
----> 1 twice1(None)

<ipython-input-161-ba865fe1e32f> in twice1(x)
      1 def twice1(x):
----> 2     print(2*x)
      3 
      4 def twice(x):
      5     return 2*x

TypeError: unsupported operand type(s) for *: 'int' and 'NoneType'

def count_digits(number):
    digits = str(number)
    return len(digits)

count_digits(2**1000)

302

More about functions¶

Functions in python are ordinary just like any ohter data type like integers, floats, lists... But that makes them special

def func(x):
    return 2*x

func

<function __main__.func>

print(func)

<function func at 0x7fa3140d7510>

type(func)

function

type(4)

int

type([1,2,3,4])

list

twotimes = func

func(5)

10

twotimes(5)

10

twotimes

<function __main__.func>

type(twotimes)

function

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

def square(x):
    return x*x

def sumofsquares(x,y):
    return square(x) + square(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(5,6)

61

sumof(square, 5, 6)

61

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

adder5 = make_adder(5)

adder5

<function __main__.make_adder.<locals>.add>

adder5(8)

13

adder5(9)

14

adder6 = make_adder(6)

adder6(9)

15

def f(a):
    return a+a

f

<function __main__.f>

adder6 = make_adder(6)

adder6

<function __main__.make_adder.<locals>.add>

adder6(7)

13

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

f = lambda x,y: x+y

f

<function __main__.<lambda>>

f(4,5)

9

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

adder7 = make_adder(7)

adder7(10)

17

print(f)

<function <lambda> at 0x7fa31407c268>

type(f)

function

Passing functions as parameter is so usefull, that in built python functions make use of it at many places

max(0,42)

42

max([0,1,2,3,5])

5

max(["one", "two", "three", "four"])# what would be output?

'two'

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

max(words, key=len)# this is how I find longest word

'three'

min(words, key=len) #this is how I find shortest word

'one'

scoresheet = [("vinay",8.8),
              ("vijay",8.9),
              ("vijaya",9.0),
              ("vilas",7.8),
              ("vishakha",9.1)
             ]

scoresheet

[('vinay', 8.8),
 ('vijay', 8.9),
 ('vijaya', 9.0),
 ('vilas', 7.8),
 ('vishakha', 9.1)]

def get_score(record):
    return record[1]

max(scoresheet, key=get_score)

('vishakha', 9.1)

min(scoresheet, key=get_score)

('vilas', 7.8)

max(scoresheet, key=get_score)[0]

'vishakha'

max(scoresheet, key=get_score)[1]

9.1

Methods from objects¶

Built in obejcts have udefull functions built in as part of object itself. These functions are called methods

book = "Alice in wonderland"

book.lower()

'alice in wonderland'

book.upper()

'ALICE IN WONDERLAND'

book.count("n")

3

book.split(" ")

['Alice', 'in', 'wonderland']

book.replace(" ", "_")

'Alice_in_wonderland'

book

'Alice in wonderland'

book.replace(" ","_").split("_")

['Alice', 'in', 'wonderland']

book.startswith("Alice")

True

book.endswith("land")

True

lists¶

numbers = list(range(5, 25, 2))

numbers

[5, 7, 9, 11, 13, 15, 17, 19, 21, 23]

numbers.count(5)

1

numbers.reverse()

numbers

[23, 21, 19, 17, 15, 13, 11, 9, 7, 5]

numbers.append(3)

numbers

[23, 21, 19, 17, 15, 13, 11, 9, 7, 5, 3]

numbers.pop()

3

numbers

[23, 21, 19, 17, 15, 13, 11, 9, 7, 5]

numbers.pop(0)

23

numbers

[21, 19, 17, 15, 13, 11, 9, 7, 5]

numbers.sort()

numbers

[5, 7, 9, 11, 13, 15, 17, 19, 21]

numbers.sort(reverse=True)

numbers

[21, 19, 17, 15, 13, 11, 9, 7, 5]

words = ["One","two","Three"]

max(words, key=lambda w:w.lower())

'two'

sorted(numbers, key=lambda x:x, reverse=True)

[21, 19, 17, 15, 13, 11, 9, 7, 5]

numbers.extend([3,1])

numbers

[21, 19, 17, 15, 13, 11, 9, 7, 5, 3, 1]

numbers.index(15)

3

tuples¶

numbers = (1,1,2,3,5,8)

numbers.count(1)

2

numbers.index(3)

3

problem

Write a function count_zeros which will count zeros in given number

>>> count_zeros(1000)
3

Write a function head that takes a list of words and n as an argument and returns first n words by dictionary order

head(["python", "lisp", "haskell", "ark", "java", "ocamel"], 3)
['ark', 'haskell', 'java']

bonus problem

write a function rearrangemax that takes an integer as an argument and returns a new integer with digits rearranged from max to min.
```
rearrangemax(43567)
76543
```

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

count_zeros(1000)

3

def head(data, n):
    return sorted(data)[:n]

head(["python", "lisp", "haskell", "ark", "java", "ocamel"],3)

['ark', 'haskell', 'java']

def rearragemax(n):
    digits = str(n)
    sorteddigits = sorted(digits, key=int, reverse=True)
    return int("".join(sorteddigits))

rearragemax(343524)

544332

modules¶

import math

def area_circle(radius):
    return math.pi*radius*radius

def polar_to_rectangular(radius, theta):
    return radius*math.cos(theta), radius*math.sin(theta)

area_circle(1)

3.141592653589793

x, y = polar_to_rectangular(1, math.pi/2)

print(x, y)

6.123233995736766e-17 1.0

import os

os.getcwd()

'/home/vikrant/trainings/2017/arcesium-oct-python'

os.getenv("HOME")

'/home/vikrant'

os.mkdir("/tmp/test1")

!ls /tmp/

config-err-tgKHDJ
firefox_vikrant
mintUpdate
ssh-oQgxr2OpAizg
systemd-private-f443c63d224a4f4d9e3c0415e5f622e1-colord.service-bEyWJv
systemd-private-f443c63d224a4f4d9e3c0415e5f622e1-rtkit-daemon.service-LW9Bft
test1

print(math)

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

os.listdir("/tmp/")

['.XIM-unix',
 'systemd-private-f443c63d224a4f4d9e3c0415e5f622e1-colord.service-bEyWJv',
 '.font-unix',
 'systemd-private-f443c63d224a4f4d9e3c0415e5f622e1-rtkit-daemon.service-LW9Bft',
 'firefox_vikrant',
 'ssh-oQgxr2OpAizg',
 '.ICE-unix',
 '.X11-unix',
 'test1',
 '.X0-lock',
 '.Test-unix',
 'config-err-tgKHDJ',
 'mintUpdate']

math

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

type(math)

module

os.path.exists("/tmp")

True

os.path.getsize("./day1.html")

419342

problem

Write a function countfiles to find number of files in given directory.
```
>>> countfiles("/tmp")
13
```
Write a function biggestfile to find a file of maximum size in given directory.
```
>>> biggestfile(os.getcwd())
day1.html
```

def countfiles(location):
    return len(os.listdir(location))

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

biggestfile(os.getcwd())

'day1.html'

Writing cutom module¶

%%file mymodule.py
import sys

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

Writing mymodule.py

import mymodule

mymodule.say_hello("Python")

Hello Python

%%file mymodule1.py
import sys

print(sys.argv)

Writing mymodule1.py

!python mymodule1.py arg1 arg2 arg3

['mymodule1.py', 'arg1', 'arg2', 'arg3']

%%file mymodule2.py
import sys

print(sys.argv)

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

def mult(x,y):
    return x*y

print(mult(3,4))

Overwriting mymodule2.py

!python mymodule2.py

['mymodule2.py']
12

%%file circle.py
import sys

a = 3
pi = 3.14

def area(r):
    return pi*r*r

def perimeter(r):
    return 2*pi*r

radius = float(sys.argv[1])
print("Area of a circle :", area(radius))
print("Perimenter of a circle:", perimeter(radius))

Overwriting circle.py

!python circle.py 10 20

Area of a circle : 314.0
Perimenter of a circle: 62.800000000000004

%%file rectangle.py
import sys

def area(l, w):
    return l*w

def perimeter(l, w):
    return 2*(l+w)

length = float(sys.argv[1])
width = float(sys.argv[2])

print("Area of rectangle :", area(length, width))
print("Perimenter of rectangle:", perimeter(length, width))

Writing rectangle.py

!python rectangle.py 2 5

Area of rectangle : 10.0
Perimenter of rectangle: 14.0

import rectangle

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-319-4efccc52c587> in <module>()
----> 1 import rectangle

/home/vikrant/trainings/2017/arcesium-oct-python/rectangle.py in <module>()
      7     return 2*(l+w)
      8 
----> 9 length = float(sys.argv[1])
     10 width = float(sys.argv[2])
     11 

ValueError: could not convert string to float: '-f'

%%file main.py

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

def sub(x,y):
    return x-y

print(__name__)

Writing main.py

!python  main.py

__main__

import main

main

main.sub(3,4)

-1

main.add(2,3)

5

from main import add

from os.path import getsize

from math import pi

help(getsize)

Help on function getsize in module genericpath:

getsize(filename)
    Return the size of a file, reported by os.stat().

help(math)

Help on module math:

NAME
    math

MODULE REFERENCE
    https://docs.python.org/3.6/library/math
    
    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
    location listed above.

DESCRIPTION
    This module is always available.  It provides access to the
    mathematical functions defined by the C standard.

FUNCTIONS
    acos(...)
        acos(x)
        
        Return the arc cosine (measured in radians) of x.
    
    acosh(...)
        acosh(x)
        
        Return the inverse hyperbolic cosine of x.
    
    asin(...)
        asin(x)
        
        Return the arc sine (measured in radians) of x.
    
    asinh(...)
        asinh(x)
        
        Return the inverse hyperbolic sine of x.
    
    atan(...)
        atan(x)
        
        Return the arc tangent (measured in radians) of x.
    
    atan2(...)
        atan2(y, x)
        
        Return the arc tangent (measured in radians) of y/x.
        Unlike atan(y/x), the signs of both x and y are considered.
    
    atanh(...)
        atanh(x)
        
        Return the inverse hyperbolic tangent of x.
    
    ceil(...)
        ceil(x)
        
        Return the ceiling of x as an Integral.
        This is the smallest integer >= x.
    
    copysign(...)
        copysign(x, y)
        
        Return a float with the magnitude (absolute value) of x but the sign 
        of y. On platforms that support signed zeros, copysign(1.0, -0.0) 
        returns -1.0.
    
    cos(...)
        cos(x)
        
        Return the cosine of x (measured in radians).
    
    cosh(...)
        cosh(x)
        
        Return the hyperbolic cosine of x.
    
    degrees(...)
        degrees(x)
        
        Convert angle x from radians to degrees.
    
    erf(...)
        erf(x)
        
        Error function at x.
    
    erfc(...)
        erfc(x)
        
        Complementary error function at x.
    
    exp(...)
        exp(x)
        
        Return e raised to the power of x.
    
    expm1(...)
        expm1(x)
        
        Return exp(x)-1.
        This function avoids the loss of precision involved in the direct evaluation of exp(x)-1 for small x.
    
    fabs(...)
        fabs(x)
        
        Return the absolute value of the float x.
    
    factorial(...)
        factorial(x) -> Integral
        
        Find x!. Raise a ValueError if x is negative or non-integral.
    
    floor(...)
        floor(x)
        
        Return the floor of x as an Integral.
        This is the largest integer <= x.
    
    fmod(...)
        fmod(x, y)
        
        Return fmod(x, y), according to platform C.  x % y may differ.
    
    frexp(...)
        frexp(x)
        
        Return the mantissa and exponent of x, as pair (m, e).
        m is a float and e is an int, such that x = m * 2.**e.
        If x is 0, m and e are both 0.  Else 0.5 <= abs(m) < 1.0.
    
    fsum(...)
        fsum(iterable)
        
        Return an accurate floating point sum of values in the iterable.
        Assumes IEEE-754 floating point arithmetic.
    
    gamma(...)
        gamma(x)
        
        Gamma function at x.
    
    gcd(...)
        gcd(x, y) -> int
        greatest common divisor of x and y
    
    hypot(...)
        hypot(x, y)
        
        Return the Euclidean distance, sqrt(x*x + y*y).
    
    isclose(...)
        isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0) -> bool
        
        Determine whether two floating point numbers are close in value.
        
           rel_tol
               maximum difference for being considered "close", relative to the
               magnitude of the input values
            abs_tol
               maximum difference for being considered "close", regardless of the
               magnitude of the input values
        
        Return True if a is close in value to b, and False otherwise.
        
        For the values to be considered close, the difference between them
        must be smaller than at least one of the tolerances.
        
        -inf, inf and NaN behave similarly to the IEEE 754 Standard.  That
        is, NaN is not close to anything, even itself.  inf and -inf are
        only close to themselves.
    
    isfinite(...)
        isfinite(x) -> bool
        
        Return True if x is neither an infinity nor a NaN, and False otherwise.
    
    isinf(...)
        isinf(x) -> bool
        
        Return True if x is a positive or negative infinity, and False otherwise.
    
    isnan(...)
        isnan(x) -> bool
        
        Return True if x is a NaN (not a number), and False otherwise.
    
    ldexp(...)
        ldexp(x, i)
        
        Return x * (2**i).
    
    lgamma(...)
        lgamma(x)
        
        Natural logarithm of absolute value of Gamma function at x.
    
    log(...)
        log(x[, base])
        
        Return the logarithm of x to the given base.
        If the base not specified, returns the natural logarithm (base e) of x.
    
    log10(...)
        log10(x)
        
        Return the base 10 logarithm of x.
    
    log1p(...)
        log1p(x)
        
        Return the natural logarithm of 1+x (base e).
        The result is computed in a way which is accurate for x near zero.
    
    log2(...)
        log2(x)
        
        Return the base 2 logarithm of x.
    
    modf(...)
        modf(x)
        
        Return the fractional and integer parts of x.  Both results carry the sign
        of x and are floats.
    
    pow(...)
        pow(x, y)
        
        Return x**y (x to the power of y).
    
    radians(...)
        radians(x)
        
        Convert angle x from degrees to radians.
    
    sin(...)
        sin(x)
        
        Return the sine of x (measured in radians).
    
    sinh(...)
        sinh(x)
        
        Return the hyperbolic sine of x.
    
    sqrt(...)
        sqrt(x)
        
        Return the square root of x.
    
    tan(...)
        tan(x)
        
        Return the tangent of x (measured in radians).
    
    tanh(...)
        tanh(x)
        
        Return the hyperbolic tangent of x.
    
    trunc(...)
        trunc(x:Real) -> Integral
        
        Truncates x to the nearest Integral toward 0. Uses the __trunc__ magic method.

DATA
    e = 2.718281828459045
    inf = inf
    nan = nan
    pi = 3.141592653589793
    tau = 6.283185307179586

FILE
    /home/vikrant/usr/local/anaconda3/lib/python3.6/lib-dynload/math.cpython-36m-x86_64-linux-gnu.so

help(circle)

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-332-ba8c55c95943> in <module>()
----> 1 help(circle)

NameError: name 'circle' is not defined

help(main)

Help on module main:

NAME
    main

FUNCTIONS
    add(x, y)
    
    sub(x, y)

FILE
    /home/vikrant/trainings/2017/arcesium-oct-python/main.py

import random

help(random.choice)

Help on method choice in module random:

choice(seq) method of random.Random instance
    Choose a random element from a non-empty sequence.

sentence = "The beauty of pascal trianlge is that it is simple yet mathematically rich"

random.choice(sentence.split())

'it'

random.choice(sentence.split())

'it'

help("".split)

Help on built-in function split:

split(...) method of builtins.str instance
    S.split(sep=None, maxsplit=-1) -> list of strings
    
    Return a list of the words in S, using sep as the
    delimiter string.  If maxsplit is given, at most maxsplit
    splits are done. If sep is not specified or is None, any
    whitespace string is a separator and empty strings are
    removed from the result.

problems

Write a python script square.py which takes an integer as an argument and prints square of that number
Write a python script add.py which takes two integers from commandline and prints addition of those numbers
Write a python script echo.py which is roughly equivalent to unix command echo. echo just prints the input string to standard output

%%file square.py
import sys

def square(x):
    return x*x

n = int(sys.argv[1])
print(square(n))

Writing square.py

!python square.py 4

16

%%file add.py
import sys

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

a = int(sys.argv[1])
b = int(sys.argv[2])
print(add(a,b))

Writing add.py

!python add.py 5 6

11

%%file echo.py
import sys

print(" ".join(sys.argv[1:]))

Overwriting echo.py

!python echo.py hello this is echo

hello this is echo

Environment¶

a = 2.0 + 3.0

a

5.0

import math

import math as m

m

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

cash = 10000
balance = 50000

def withdraw(balance, amount):
    balance = balance - amount
    return balance

cash = withdraw(balance, 1000)
print("balance = ", balance)
print("cash =", cash)

withdraw(60000, 2000)
print(balance)

balance =  50000
cash = 49000
50000

Conditions¶

1 > 2

False

1.99 <= 2.0

True

2 != 3

True

2 <= 2

True

"python" > "java"

True

"alice" in "alice in wonderland"

True

"alice" not in "alice in wonderland"

False

book = "alice in wonderland"

book.startswith("alice")

True

book.endswith("land")

True

def is_python_script(filename):
    return filename.endswith(".py")

is_python_script("hello.py")

True

python = [3.4, "if"]
if "if" in python:
    print("Obviously python has if")
elif python[0] > 3:
    print("python can have long list of elifs")
elif len(python) > 1:
    print("still ...long")
else:
    print("it will come here if none of above condition is True")

Obviously python has if

def even(n):
    if n%2 == 0:
        return True
    else:
        return False

even(5)

False

The conditional after if is True for

For nonzero integer value
for object that is not None
for nonempty sequences

def even(n):
    return not n%2

even(2)

True

def odd(n):
    return not even(n)

odd(3)

True

Do it yourself

Write a python function filetype which will take filename as argument and return file type. it should recognise following file types. If filetype is not from given list , it should return None

    type     extension
    python   .py
    java     .java
    c        .c
    text     .txt

>>> filetype("square.py")
python
>>> filetype("square.txt")
text

Write a function minimum (without using in build function min) to find minimum of two numbers
```
>>> minimum(3,4)
3
```
write a function minimum3 to find minimum of three numbers
```
minimum3(2,3,4)
2
```

def minimum(a,b):
    if a < b:
        return a
    else:
        return b
    
def minimum3(x,y,z):
    return minimum(minimum(x,y), z)

minimum3(3,4,5)

3

primes = [2,3,5,7,11,13,17]

5 in primes

True

primes2 = primes

primes is primes2

True

primes == primes2

True

prime3 = list(primes)

prime3 == primes

True

prime3 is primes

False

a = "abcd"

b = a

a.replace("ab", "ef")

'efcd'

a

'abcd'

b

'abcd'

a.sort()

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-392-e7eb8b51a6fa> in <module>()
----> 1 a.sort()

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