Lecture3- Quick Tour

What will learn today?

• Writing your own functions
• useful methods and builtins
• Variable namespace

online notes for this session

len([1,2,3,45])

4

len("test")

4

len({"a":23,"b":34})

2

str(54565)

'54565'

z = int(input("Eneter value of z:"))

Custom functions

def foo(name): # defination function should begin with def, should end :
print("Hello", name)

  File "<ipython-input-7-1784cac0f0f9>", line 2
    print("Hello", name)
    ^
IndentationError: expected an indented block

def foo(name): # defination function should begin with def, should end :
    print("Hello", name)

foo("Vikrant")

Hello Vikrant

foo("PCCOE")

Hello PCCOE

def area_circle(radius):
    return 3.14*radius**2

area_circle(1)

3.14

def twice(x):
    return 2*x

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

twice(5)

10

twice1(5)

10

x_2 = twice(5)

print(x_2)

10

x_2_ = twice1(5)

10

print(x_2_)

None

twice(twice(5))

20

twice1(twice1(5))

10

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-24-9c16ec1a24f8> in <module>
----> 1 twice1(twice1(5))

<ipython-input-14-22e986a8fae6> in twice1(x)
      1 def twice1(x):
----> 2     print(2*x)

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

len(str(42**100))

163

Assignment operator

x = 15 

x

15

x + 3

18

foo

<function __main__.foo(name)>

x

15

Methods

Methods are something like a function, but not a function.

sentence = "These are few wise words!"

sentence.startswith("T") # it returns boolean, True if sentence starts with whatever argument is passed

True

sentence.startswith("N")

False

sentence.endswith("words")

False

sentence.endswith("words!")

True

sentence.endswith("Words!") # it is case sensitive

False

sentence.isupper()

False

"THIS".isupper()

True

"THIS".islower()

False

sentence.isalnum()

False

"this_is_alphanumric".isalnum()

False

"user123".isalnum()

True

"hello".capitalize()

'Hello'

sentence.capitalize()

'These are few wise words!'

sentence.upper()

'THESE ARE FEW WISE WORDS!'

sentence.lower()

'these are few wise words!'

sentence # calling any method will not change original string! because string is immutable object

'These are few wise words!'

sentence.rjust(50)

'                         These are few wise words!'

sentence.ljust(50)

'These are few wise words!                         '

sentence.center(50)

'            These are few wise words!             '

sentence.center(100)

'                                     These are few wise words!                                      '

sentence.replace("wise", "foolish")

'These are few foolish words!'

foolish = sentence.replace("wise", "foolish")

print(sentence)

These are few wise words!

print(foolish)

These are few foolish words!

sentence.split() # will split  the string on white spaces into multiple string

['These', 'are', 'few', 'wise', 'words!']

path = "c:\\Prgram Files\\Python"

path.split("\\")

['c:', 'Prgram Files', 'Python']

path = "/home/yoouhome/Documents"

path.split("/")

['', 'home', 'yoouhome', 'Documents']

"_".join(["one","two","three","four"])

'one_two_three_four'

"/".join(['','home','vikrant','Documents'])

'/home/vikrant/Documents'

Questions

• convert the sentence, with a string that has _ betweeen every word instead of space.

line = " this is first line from file     "

line.strip() # trailing whitespaces from both ends

'this is first line from file'

line.rstrip()

' this is first line from file'

line.lstrip()

'this is first line from file     '

line.strip().split()

['this', 'is', 'first', 'line', 'from', 'file']

line.strip.split()[-1]

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-78-4c6ea2f3f972> in <module>
----> 1 line.strip.split()[-1]

AttributeError: 'builtin_function_or_method' object has no attribute 'split'

line.strip().split()[-1] # last word from a sentence

'file'

List methods

nums = list(range(1,5))

nums

[1, 2, 3, 4]

nums.index(3)

2

nums.index(4)

3

names = ["Aparna","Arpita","Ana","Alice"]

names.index("Alice")

3

names.count("Ana")

1

ones = [1, 1, 1,1 , 1]

ones.count(1)

5

empty = []

empty.append(1) # it has changes original list

empty

[1]

empty.insert(0, 34)

empty

[34, 1]

empty.insert(1, 45)

empty

[34, 45, 1]

empty.extend([0, 0, 0])

empty

[34, 45, 1, 0, 0, 0]

empty.remove(0) # remove first occurence of 0

empty

[34, 45, 1, 0, 0]

empty.remove(45)

empty

[34, 1, 0, 0]

c = nums.count(1)

c

1

y = empty.insert(1, 10)

print(y)

None

empty

[34, 10, 1, 0, 0]

x = nums.pop() # it will remove last item , but also retun the removed item

nums

[1, 2, 3]

x

4

digits = [0, 1, 2, 3, 4, 5]

digits.clear()

digits

[]

empty.sort() # it will sort inplace, so original list is no more available

empty

[0, 0, 1, 10, 34]

Questions

• Write a function to find number of words from given text

  >>> count_words("this has four words")
  4

• Write a function to find only filename from given path of a file

  >>> path = "/home/vikrant/Documents/hello.py"
  >>> filename(path)
  'hello.py'

def count_words(text):
    words = text.split()
    return len(words)

def filename(path):
    """returns filename from given path.
    assumes unix style of path
    """
    tokens = path.split("/")
    return tokens[-1]

count_words("this is some big sentence with some words in it")

10

filename("/home/vikrant/hello.txt")

'hello.txt'