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-Hello friends and welcome to the tutorial on Basic Data types and
-operators in Python.
-{{{ Show the slide containing title }}}
-
-{{{ Show the slide containing the outline slide }}}
-
-In this tutorial, we shall look at::
-
- * Various Datatypes in Python
- * Operators with a little hands-on on how they can be applied to
- the different data types.
-
-
-
-First we will explore python data structures in the domain of numbers.
-There are three built-in data types in python to represent numbers.
-
-{{{ A slide to make a memory note of this }}}
-
-These are:
-
- * Integers
- * Complex and
- * Boolean
-
-Lets first talk about integers. ::
-
- a = 13
- a
-
-
-Thats it, there we have our first integer variable a.
-
-
-
-If we now see ::
-
- type(a)
- <type 'int'>
-
-This means that a is a type of int. Being an int data structure
-in python means that there are various functions that this variable
-has to manipulate it different ways. You can explore these by doing,
-
- a.<Tab>
-
-
-
-Lets see the limits of this int.
-
- b = 99999999999999999999
- b
-
-As you can see even when we put a value of 9 repeated 20 times
-python did not complain. However when you asked python to print
-the number again it put a capital L at the end. Now if you check
-the type of this variable b, ::
-
- type(b)
- <type 'long'>
-
-
-The reason for this is that python recognizes large integer numbers
-by the data type long. However long type and integer type share there
-functions and properties.
-
-Lets now try out the second type in list called float.
-
-Decimal numbers in python are recognized by the term float ::
-
- p = 3.141592
- p
-
-If you notice the value of output of p isn't exactly equal to p. This
-is because computer saves floating point values in a specific
-format. There is always an aproximationation. This is why we should
-never rely on equality of floating point numbers in a program.
-
-The last data type in the list is complex number ::
-
- c = 3.2+4.6j
-
-as simple as that so essentialy its just a combination of two floats the
-imaginary part being define by j notation instead of i. Complex numbers have a lot of functions specific to them.
-Lets check these ::
-
- c.<Tab>
-
-Lets try some of them ::
-
- c.real
- c.imag
-
-c.real gives the real part of the number and c.imag the imaginary.
-
-We can get the absolute value using the function ::
-
- abs(c)
-
-Python also has Boolean as a built-in type.
-
-Try it out just type ::
-
- t = True
-
-note that T in true is capitalized.
-
-You can apply different Boolean operations on t now for example ::
-
- f = not t
- f
- f or t
- f and t
-
-
-
-The results are explanotary in themselves.
-
-The usage of boolean brings us to an interesting question of precendence.
-What if you want to apply one operator before another.
-
-Well you can use parenthesis for precedence.
-
-Lets write some piece of code to check this out.
-
- In[]: a=False
- In[]: b=True
- In[]: c=True
-
-To check how precedence changes with parenthesis. We will try two
-expressions and their evaluation.
-
-one ::
-
- (a and b) or c
-
-This expression gives the value True
-
-where as the expression ::
-
- a and (b or c)
-
-gives the value False.
-
-Lets now discuss sequence data structures in python. Sequence
-datatypes are those in which elements are kept in a sequential
-order. All the elements accessed using index.
-
-{{{ slide to for memory aid }}}
-
-The sequence datatypes in python are ::
-
- * list
- * string
- * tuple
-
-The list type is a container that holds a number of other
-objects, in the given order.
-
-We create our first list by typing ::
-
- num_list = [1, 2, 3, 4]
- num_list
-
-
-Items enclosed in square brackets separated by comma
-constitutes a list.
-
-Lists can store data of any type in them.
-
-We can have a list something like ::
-
- var_list = [1, 1.2, [1,2]]
- var_list
-
-
-
-Now we will have a look at strings
-
-type ::
-
- In[]: greeting_string="hello"
-
-
-greeting_string is now a string variable with the value "hello"
-
-{{{ Memory Aid Slide }}}
-
-Python strings can actually be defined in three different ways ::
-
- In[]: k='Single quote'
- In[]: l="Double quote contain's single quote"
- In[]: m='''"Contain's both"'''
-
-Thus, single quotes are used as delimiters usually.
-When a string contains a single quote, double quotes are used as delimiters.
-When a string quote contains both single and double quotes, triple quotes are
-used as delimiters.
-
-The last in the list of sequence data types is tuple.
-
-To create a tuple we use normal brackets '('
-unlike '[' for lists.::
-
- In[]: num_tuple = (1, 2, 3, 4, 5, 6, 7, 8)
-
-Because of their sequential property there are certain functions and
-operations we can apply to all of them.
-
-{{{ Slide for memory aid }}}
-
-The first one is accessing.
-
-They can be accessed using index numbers ::
-
- In[]: num_list[2]
- In[]: num_list[-1]
- In[]: greeting_string[1]
- In[]: greeting_string[3]
- In[]: greeting_string[-2]
- In[]: num_tuple[2]
- In[]: num_tuple[-3]
-
-
-Indexing starts from 0 from left to right and from -1 when accessing
-lists in reverse. Thus num_list[2] refers to the third element 3.
-and greetings [-2] is the second element from the end , that is 'l'.
-
-
-
-Addition gives a new sequence containing both sequences ::
-
- In[]: num_list+var_list
- In[]: a_string="another string"
- In[]: greeting_string+a_string
- In[]: t2=(3,4,6,7)
- In[]: num_tuple+t2
-
-len function gives the length ::
-
- In[]: len(num_list)
- In[]: len(greeting_string)
- In[]: len(num_tuple)
-
-Prints the length the variable.
-
-We can check the containership of an element using the 'in' keyword ::
-
- In[]: 3 in num_list
- In[]: 'H' in greeting_string
- In[]: 2 in num_tuple
-
-We see that it gives True and False accordingly.
-
-Find maximum using max function and minimum using min::
-
- In[]: max(num_tuple)
- In[]: min(greeting_string)
-
-Get a sorted list and reversed list using sorted and reversed function ::
-
- In[]: sorted(num_list)
- In[]: reversed(greeting_string)
-
-As a consequence of the order one we access a group of elements together.
-This is called slicing and striding.
-
-First Slicing
-
-Given a list ::
-
- In[]:j=[1,2,3,4,5,6]
-
-Lets say we want elements starting from 2 and ending in 5.
-
-For this we can do ::
-
- In[]: j[1:4]
-
-The syntax for slicing is sequence variable name square bracket
-first element index, colon, second element index.The last element however is notincluded in the resultant list::
-
-
- In[]: j[:4]
-
-If first element is left blank default is from beginning and if last
-element is left blank it means till the end.
-
- In[]: j[1:]
-
- In[]: j[:]
-
-This effectively is the whole list.
-
-Striding is similar to slicing except that the step size here is not one.
-
-Lets see by example ::
-
- new_num_list=[1,2,3,4,5,6,7,8,9,10]
- new_num_list[1:8:2]
- [2, 4, 6, 8]
-
-The colon two added in the end signifies all the alternate elements. This is why we call this concept
-striding because we move through the list with a particular stride or step. The step in this example
-being 2.
-
-We have talked about many similar features of lists, strings and tuples. But there are many important
-features in lists that differ from strings and tuples. Lets see this by example.::
-
- In[]: new_num_list[1]=9
- In[]: greeting_string[1]='k'
-
-{{{ slide to show the error }}}
-
-
-
-As you can see while the first command executes with out a problem there is an error on the second one.
-
-Now lets try ::
-
- In[]: new_tuple[1]=5
-
-Its the same error. This is because strings and tuples share the property of being immutable.
-We cannot change the value at a particular index just by assigning a new value at that position.
-
-
-We have looked at different types but we need to convert one data type into another. Well lets one
-by one go through methods by which we can convert one data type to other:
-
-We can convert all the number data types to one another ::
-
- i=34
- d=float(i)
- d
-
-Python has built in functions int, float and complex to convert one number type
-data structure to another.
-
- dec=2.34
- dec_con=int(dec)
- dec_con
-
-
-As you can see the decimal part of the number is simply stripped to get the integer.::
-
- com=2.3+4.2j
- float(com)
- com
-
-In case of complex number to floating point only the real value of complex number is taken.
-
-Similarly we can convert list to tuple and tuple to list ::
-
- lst=[3,4,5,6]
- tup=tuple(lst)
- tupl=(3,23,4,56)
- lst=list(tuple)
-
-However string to list and list to string is an interesting problem.
-Lets say we have a string ::
-
- In: somestring="Is there a way to split on these spaces."
- In: somestring.split()
-
-
-This produces a list with the string split at whitespace.
-similarly we can split on some other character.
-
- In: otherstring="Tim,Amy,Stewy,Boss"
-
-How do we split on comma , simply pass it as argument ::
-
- In: otherstring.split(',')
-
-join function does the opposite. Joins a list to make a string.::
-
- In[]:','.join['List','joined','on','commas']
-
-Thus we get a list joined on commas. Similarly we can do spaces.::
-
- In[]:' '.join['Now','on','spaces']
-
-Note that the list has to be a list of strings to apply join operation.
-
-.. #[Nishanth]: string to list is fine. But list to string can be left for
- string manipulations. Just say it requires some string
- manipulations and leave it there.
-
-.. #[Nishanth]: Where is the summary
- There are no exercises in the script
-
-{{{ Show the "sponsored by FOSSEE" slide }}}
-
-This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India
-
-Hope you have enjoyed and found it useful.
-
-Thank You.
-
-
-
-Author : Amit Sethi
-Internal Reviewer 1 : Nishanth
-Internal Reviewer 2 :
-External Reviewer