More Data Types

String

String is a sequence of characters.
We have seen the string representation in previous chapter.
Python provides lots of built in method associated with it.

Side by side string literals

>>> a = 'foo' 'bar'
>>> a
'foobar'
>>> a = "foo"
>>> a * 5
'foofoofoofoofoo'

Have fun with string associated methods

>>> s = "chandan kumar"
>>> s.title() # returns a title case
'Chandan Kumar'
>>> z = s.upper() # Converts it to upper case
>>> z
'CHANDAN KUMAR'
>>> z.lower() # converts to lower case
'chandan kumar'
>>> s = "I am A FunnY ProgRAmmER"
>>> s.swapcase() # converts it to swapcase
'i AM a fUNNy pROGraMMer'
>>> s = "chkumar246 Kumar"
>>> s.isalpha() # Check for alphabets
False
>>> y = "chkumar"
>>> y.isalpha()
True
>>> y = '1234'
>>> y.isdigit() # check all characters are digit or not
True
>>> s = "Chandan Kumar"
>>> s.istitle() # check for title
True
>>> s = "PUNE"
>>> s.isupper() # Check for all characters are in uppercase
True
>>> s = 'pune'
>>> s.islower() # Check for all characters are in lowercase
True

Let's split and Join a string

>>> a = 'We are learning Python'
>>> a.split()
['We', 'are', 'learning', 'Python']
>>> a.split() # Split the string based on spaces
['We', 'are', 'learning', 'Python']
>>> a.split('a') # Split the string at character *a*
['We ', 're le', 'rning Python']
>>> data = a.split()
>>> data
['We', 'are', 'learning', 'Python']
>>> type(data)
<class 'list'>
>>> # split() method always returns a list
... 
>>> # A list can be joined by join method.
... 
>>> a
'We are learning Python'
>>> "**".join("We are learning".split())
'We**are**learning'
>>>

Strip some characters from a string

>>> a = "abc\n"
>>> a.strip() # It will remove new line 
'abc'
>>> b = "https://facebook.com"
>>> b.lstrip('https://') # strip from left side
'facebook.com'
>>> b.rstrip(".com") # strip from right side
'https://facebook'
>>> domain_name = b.lstrip('https://').rstrip('.com')
>>> domain_name
'facebook'
>>>

Some more functions with string

>>> b
'https://facebook.com'
>>> '.com' in b
True
>>> len(b)
20

String Indexing

First character of a string has index 0.
Negative indices start form -1, when counted from right.

>>> word = "Welcome to FOSS MEET"
>>> word[0]
'W'
>>> word[-1]
'T'
>>> word[5]
'm'
>>> word[-3]
'E'

String Slicing

string[x:y] returns the string starting from index x to y-1.

>>> word[2:8]
'lcome '
>>> word[8]
't'

String are immutable

It means we cannot update the characters of a string.

>>> word[5] = 'b'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

List

Comma separated values between square brackets
List can be sliced, indexed and concatenated
Lists are mutable it means we can append and remove items from a list.

>>> a = [1,2,3,4,5,6]
>>> a[0]
1
>>> a[-1]
6
>>> a[6]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range
>>> a.append(1000)
>>> a
[1, 2, 3, 4, 5, 6, 1000]
>>> a[6]
1000
>>> b = ['hello', 'foo', 'bar']
>>> a + b
[1, 2, 3, 4, 5, 6, 1000, 'hello', 'foo', 'bar']
>>> a.remove(5)
>>> a
[1, 2, 3, 4, 6, 1000]
>>> ## nesting list
... 
>>> a = [1, 2, 3]
>>> b = ['foo', 'bar']
>>> nested_list = [a, b]
>>> nested_list
[[1, 2, 3], ['foo', 'bar']]
>>> nested_list[0]
[1, 2, 3]
>>> nested_list[1][-1]
'bar'
>>> len(a)
3
>>> 1 in a
True
>>> a = ['foo', 'bar', 'alpha']
>>> del a[1]
>>> a
['foo', 'alpha']
>>> len(a)
2
>>> 'foo' in a
True

List Comprehensions

List comprehensions provide a concise way to create lists. Each list comprehension consists of an expression followed by a for clause, then zero or more for or if clauses. The result will be a list resulting from evaluating the expression in the context of the for and if clauses which follow it.

>>> square_of_10 = [i ** 2 for i in range(11)]
>>> square_of_10
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Tuples

Items separated by comma in a closed bracket.
These are immutable, it means we cannot append or remove data from it.

>>> a = (1,2,3,'hello')
>>> a
(1, 2, 3, 'hello')
>>> type(a)
<class 'tuple'>
>>> a[2]
3
>>> a[-1]
'hello'
>>> divmod(15,2)
(7, 1)
>>> x, y = divmod(15, 2)
>>> x
7
>>> y
1
>>> del a[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object doesn't support item deletion
>>> a = (100)
>>> type(a)
<class 'int'>
>>> # to create a tuple with single item
... 
>>> a = (100,)
>>> type(a)
<class 'tuple'>

Set

A list of items with no duplicates in curly braces.

>>> a = 'axbecjnn2226'
>>> set(a)
{'n', 'e', 'a', '6', 'x', 'b', 'j', '2', 'c'}
>>>

Define another set b and try out a - b, a | b, a & b, a ^ b
We can also add and remove values from set

>>> c
{'n', 'e', 'a', '6', 'x', 'b', 'j', '2', 'c'}
>>> c.add('hello')
>>> c
{'n', 'e', 'a', 'hello', '6', 'x', 'b', 'j', '2', 'c'}
>>> c.pop()
'n'

Dictionaries

Unordered set of key: value pairs under {} braces.
Keys are unique in nature.
Dictionaries are mutable but keys must be of immutable type.
By using particular key, we can access or update the value.
Values can be of any data type.

>>> mydict = {'number': 1, 'letter': 'foobar', 'mytuple':(1,2,3), 'foobar': [1,2,3,4]}
>>> mydict
{'number': 1, 'letter': 'foobar', 'mytuple': (1, 2, 3), 'foobar': [1, 2, 3, 4]}
>>> mydict['letter']
'foobar'
>>> mydict['number'] = "It is really a number"
>>> mydict
{'number': 'It is really a number', 'letter': 'foobar', 'mytuple': (1, 2, 3), 'foobar': [1, 2, 3, 4]}
>>>

Methods associated with dictionaries

>>> mydict.keys()
dict_keys(['number', 'letter', 'mytuple', 'foobar'])
>>> mydict.values()
dict_values(['It is really a number', 'foobar', (1, 2, 3), [1, 2, 3, 4]])
>>> mydict.items()
dict_items([('number', 'It is really a number'), ('letter', 'foobar'), ('mytuple', (1, 2, 3)), ('foobar', [1, 2, 3, 4])])
>>> 'foobar' in mydict
True
>>> len(mydict)
4

We can always run a loop over list, string, tuple and dict:

Fun time

Create a dictionary which has keys like numbers, strings, tuples, list, set and dict and put some value.
Run a for loop and print their data types and their content.
Checkout lambda and map function