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-.. Objectives
-.. ----------
-
-.. At the end of this tutorial, you should know --
-
-.. 1. Learn about Python Data Structures and Operators.(Remembering)
-.. #.Use them to do basic operations.(Applying)
-
-.. Prerequisites
-.. -------------
-
-.. None
-
-.. Author : Amit Sethi
- Internal Reviewer :
- External Reviewer :
- Checklist OK? : <put date stamp here, if OK> [2010-10-05]
-
-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
-
-* Datatypes in Python
- * Numbers
- * Boolean
- * Sequence
-* Operators in Python
- * Arithmetic Operators
- * Boolean Operators
-
-* Python Sequence Data types
- * list
- * string
- * tuple
-
-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 the different datatypes }}}
-
-These are:
-
- * int
- * float
- * complex
-
-Lets first talk about int. ::
-
- a = 13
- a
-
-
-Now, we have our first int variable a.
-
-
-If we now see ::
-
- type(a)
- <type 'int'>
-
-This means that a is a type of int. There are lot of functions associated
-with the int datatype, to manipulate it in different ways. These can be
-explored by doing, ::
-
- a.<Tab>
-
-*int* datatype can hold integers of any size lets see this by an example.
-::
-
- b = 99999999999999999999
- b
-
-As you can see even when we put a value of 9 repeated 20 times python did
-not complain. This is because python's int data-type can hold integers of any
-size.
-
-Let us now look at the float data-type.
-
-Decimal numbers in python are represented by the float data-type ::
-
- 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 approximation. 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 defined by j notation instead of i. Complex numbers
-have a lot of functions specific to them. Let us look at 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)
-
-
-Following is are exercises that you must do.
-
-%% %% Find the absolute value of 3+4j
-::
-
- abs(3+4j)
-
-%% %% What is the datatype of number 999999999999999999? Is it
-not int?
-::
-
- Long
- Big integers are internally stored in python
- as Long datatype.
-
-Please, pause the video here. Do the exercises and then continue.
-
-
-{{ Slide for showing Boolean datatypes }}
-
-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 self explanatory.
-
-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.::
-
- a=False
- b=True
- 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.
-
-
-Let's now look at some operators available in Python to manipulate
-these data types.
-
-Python uses '+' for addition ::
-
- 23 + 74
-
-'-' for subtraction ::
-
- 23 - 56
-
-'*' for multiplication ::
-
- 45*76
-
-'/' for division ::
-
- 384/16
- 8/3
- 8.0/3
-
-When we did 8/3 the first case results in am integer
-output as both the operands are integer however when
-8.0/3 is used the answer is float as one of the operands is
-float.
-
-
-'%' for modulo operation ::
-
- 87 % 6
-
-and two stars for a exponent. ::
-
- 7**8
-
-
-In case one wishes to use the current value of variable in which the result
-is stored in the expression one can do that by putting the operator before
-`equal to`. ::
-
- a=73
- a*=34
-
-is same as ::
-
- a=a*34
-
-and ::
-
- a/=23
-
-is same as ::
-
- a=a/23
-
-Following is are exercises that you must do.
-
-%% %% Using python find sqaure root of 3?
-
-%% %% Is 3**1/2 and 3**0.5 same
-
-Please, pause the video here. Do the exercises and then continue.
-
-::
-
- 3**0.5
-
-::
- No,One gives an int answer and the other float
-
-
-Lets now discuss sequence data types in Python. Sequence data types
-are those in which elements are kept in a sequential order and all the
-elements are accessed using index numbers.
-
-{{{ slide introducing sequence datatype }}}
-
-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
-
-Lets look at another sequence data type, strings
-
-type ::
-
- greeting_string="hello"
-
-
-greeting_string is now a string variable with the value "hello"
-
-{{{ All the different types of strings shown }}}
-
-Python strings can actually be defined in three different ways ::
-
- k='Single quote'
- l="Let's see how to include a single quote"
- m='''"Let's see how to include both"'''
-
-As you can see, 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.::
-
- 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.
-
-
-
-The first one is accessing.
-
-They can be accessed using index numbers ::
-
- num_list[2]
- num_list[-1]
- greeting_string[1]
- greeting_string[3]
- greeting_string[-2]
- num_tuple[2]
- 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 ::
-
- num_list+var_list
- a_string="another string"
- greeting_string+a_string
- t2=(3,4,6,7)
- num_tuple+t2
-
-len function gives the length ::
-
- len(num_list)
- len(greeting_string)
- len(num_tuple)
-
-Prints the length the variable.
-
-We can check the containership of an element using the 'in' keyword ::
-
- 3 in num_list
- 'H' in greeting_string
- 2 in num_tuple
-
-We see that it gives True and False accordingly.
-
-Find maximum using max function and minimum using min::
-
- max(num_tuple)
- min(greeting_string)
-
-Get a sorted list ::
-
- sorted(num_list)
-
-
-As a consequence of their order, we can access a group of elements in a
-sequence, together. This is called slicing and striding.
-
-First lets discuss Slicing,
-
-Given a list ::
-
- j=[1,2,3,4,5,6]
-
-Lets say we want elements starting from 2 and ending in 5.
-
-For this we can do ::
-
- 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 not
-included in the resultant list::
-
-
- j[:4]
-
-If first element is left blank default is from beginning and if last
-element is left blank it means till the end.
-
-::
-
- j[1:]
-
- 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.::
-
- new_num_list[1]=9
- 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 ::
-
- 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 converting a string to a list and a list to a string is an
-interesting problem. Let's 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.::
-
- ','.join['List','joined','on','commas']
-
-Thus we get a list joined on commas. Similarly we can do spaces.::
-
- ' '.join['Now','on','spaces']
-
-Note that the list has to be a list of strings to apply join operation.
-
-With this we come to the end of this tutorial .
-
-Following is an (are) exercise(s) that you must do.
-
-
-
-%% %% Check if 3 is an element of the list [1,7,5,3,4]. In case
-it is change it to 21.
-::
- l=[1,7,5,3,4]
- 3 in l
- l[3]=21
- l
-
-%% %% Convert the string "Elizabeth is queen of england" to
-"Elizabeth is queen"
-::
-
- s="Elizabeth is queen of england"
- stemp=s.split()
- ' '.join(stemp[:3])
-
-Please, pause the video here. Do the exercise(s) and then continue.
-
-
-This brings us to the end of the tutorial. In this tutorial we have
-discussed
-
-1. Number Datatypes , integer,float and complex
-2. Boolean and datatype and operators
-3. Sequence data types ,List,String and Tuple
-4. Accesing sequence
-5. Slicing sequences
-6. Finding length , sorting and reversing operations on sequences.
-7. Immutability.
-
-{{{ 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.
-
-
-..
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