Python slide.1

Python Programming
Python is a high-level, interpreted, interactive and object-oriented
scripting language.
●

●

●

Python is Interpreted: This means that it is processed at runtime
by the interpreter and you do not need to compile your program
before executing it.
Python is Interactive: This means that you can actually sit at a
Python prompt and interact with the interpreter directly to write
your programs
Python is Object-Oriented: This means that Python supports
Object-Oriented style

History of Python

Python was developed by Guido van Rossum in the late
eighties and early nineties at the National Research Institute for
Mathematics and Computer Science in the Netherlands.
C++...etc

Python is derived from many other languages, including C,

Python Features
➢ Easy-to-learn: Python has relatively few keywords, simple structure,

and a clearly defined syntax. This allows the student to pick up the
language in a relatively short period of time.

➢ Easy-to-read: Python code is much more clearly defined and visible

to the eyes.

➢ Easy-to-maintain: Python's success is that its source code is fairly

easy-to-maintain.

➢ Portable: Python can run on a wide variety of hardware platforms and

has the same interface on all platforms.

➢ Extendable: You can add low-level modules to the Python interpreter.

Python Basic Syntax
The Python language has many similarities to C and Java. However, there are
some definite differences between the languages like in syntax also.

Python Identifiers:
A Python identifier is a name used to identify a variable, function, class, module
or other object. An identifier starts with a letter A to Z or a to z or an underscore
(_) followed by zero or more letters, underscores and digits (0 to 9).
Python does not allow punctuation characters such as @, $ and % within
identifiers. Python is a case sensitive programming language. Thus, Manpower
and manpower are two different identifiers in Python.

Reserved Words:
The following list shows the reserved words in Python.
These reserved words may not be used as constant or variable or any
other identifier names. All the Python keywords contain lowercase
letters only.

and
assert
break
class
continue
def
del
elif
else
except

exec
finally
for
from
global
if
import
in
is
lambda

not
or
pass
print
raise
return
try
while
with
yield

Lines and Indentation:

In python there are no braces to indicate blocks of code for
class and function definitions or flow control. Blocks of code are
denoted by line indentation.
The number of spaces in the indentation is variable, but all
statements within the block must be indented the same amount. Both
blocks in this example are fine:

Example:
if True:
print "True"
else:
print "False"
However, the second block in this example will generate an error:
if True:
print "Answer"
print "True"
else:
print "Answer"
print "False" <----Error
Thus, in Python all the continous lines indented with similar number of spaces would form a block.

Multi-Line Statements:
Statements in Python typically end with a new line. Python does, however, allow the use of the
line continuation character () to denote that the line should continue.
Example:
total = item_one +
item_two +
item_three

<----New line charactor

Statements contained within the [], {} or () brackets do not need to use the line continuation character.
Example:
days = ['Monday', 'Tuesday', 'Wednesday',
'Thursday', 'Friday']

Quotation in Python:

Python accepts single ('), double (") and triple (''' or """) quotes to denote string
literals, as long as the same type of quote starts and ends the string.The triple quotes can be used
to span the string across multiple lines

Example:
word = 'word'

<--------------- single

sentence = "This is a sentence."

<------------- double

paragraph = """This is a paragraph. It is
made up of multiple lines and sentences.""" <------------ triple

Python Variable Types
Variables are nothing but reserved memory locations to store values. This means that
when you create a variable you reserve some space in memory.
Based on the data type of a variable, the interpreter allocates memory and decides
what can be stored in the reserved memory. Therefore, by assigning different data types to
variables, you can store integers, decimals or characters in these variables.
Assigning Values to Variables:
Python variables do not have to be explicitly declared to reserve memory space.
The declaration happens automatically when you assign a value to a variable. The equal
sign (=) is used to assign values to variables.
The operand to the left of the = operator is the name of the variable and the operand
to the right of the = operator is the value stored in the variable.

Example:
counter = 100
miles = 1000.0
name = "John"

# An integer assignment
# A floating point
# A string

print counter
print miles
print name
Here, 100, 1000.0 and "John" are the values assigned to counter, miles and name variables, respectively.
While running this program, this will produce the following result:
Output:
100
1000.0
John

Multiple Assignment:
Python allows you to assign a single value to several variables simultaneously.
Example:
a=b=c=1
Here, an integer object is created with the value 1, and all three variables are assigned to
the same memory location.
You can also assign multiple objects to multiple variables. For example:
a, b, c = 1, 2, "john"

Here, two integer objects with values 1 and 2 are assigned to variables a and b, and one
string object with the value "john" is assigned to the variable c.

Python Numbers:
Number data types store numeric values. They are immutable data types which means that changing
the value of a number data type results in a newly allocated object.
Number objects are created when you assign a value to them.
For example:
var1 = 1
var2 = 10
You can delete a single object or multiple objects by using the del statement.
For example:
del var
del var_a, var_b

Python supports four different numerical types:


int



long



float



complex

int : 10 , -786
long : 51924361L , -0x19323L
float : 0.0 , -21.9
complex : 3.14j

Python Strings:
Strings in Python are identified as a contiguous set of characters in between quotation
marks. Python allows for either pairs of single or double quotes. Subsets of strings can be
taken using the slice operator ( [ ] and [ : ] ) with indexes starting at 0 in the beginning of
the string and working their way from -1 at the end.
The plus ( + ) sign is the string concatenation operator and the asterisk ( * ) is the
repetition operator.
Example:
str = 'Hello World!'
print str
print str[0]

# Prints complete string
# Prints first character of the string

print str[2:5]

# Prints characters starting from 3rd to 5th

print str[2:]

# Prints string starting from 3rd character

print str * 2

# Prints string two times

print str + "TEST" # Prints concatenated string
Output:
Hello World!
H
llo
llo World!
Hello World!Hello World!
Hello World!TEST

Python Lists:
Lists are the most versatile of Python's compound data types. A list contains items separated by
commas and enclosed within square brackets ([]).
Example:
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
tinylist = [123, 'john']
print list

# Prints complete list

print list[0]

# Prints first element of the list

print list[1:3]

# Prints elements starting from 2nd till 3rd

print list[2:]

# Prints elements starting from 3rd element

print tinylist * 2 # Prints list two times
print list + tinylist # Prints concatenated lists

Python Tuples:
A tuple is another sequence data type that is similar to the list. A
tuple consists of a number of values separated by commas. Unlike lists,
however, tuples are enclosed within parentheses.
The main differences between lists and tuples are: Lists are
enclosed in brackets ( [ ] ) and their elements and size can be changed,
while tuples are enclosed in parentheses ( ( ) ) and cannot be updated.
Example:
tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
tinytuple = (123, 'john')

print tuple

# Prints complete list

print tuple[0]

# Prints first element of the list

print tuple[1:3]

# Prints elements starting from 2nd till 3rd

print tuple[2:]

# Prints elements starting from 3rd element

print tinytuple * 2 # Prints list two times
print tuple + tinytuple # Prints concatenated lists
Output:
('abcd', 786, 2.23, 'john', 70.200000000000003)
abcd
(786, 2.23)

(2.23, 'john', 70.200000000000003)
(123, 'john', 123, 'john')
('abcd', 786, 2.23, 'john', 70.200000000000003, 123, 'john')
Following is invalid with tuple, because we attempted to update a tuple, which is
not allowed. Similar case is possible with lists:
tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
tuple[2] = 1000 # Invalid syntax with tuple
list[2] = 1000

# Valid syntax with list

Python Dictionary:
Python's dictionaries are kind of hash table type. They work like associative arrays
or hashes found in Perl and consist of key-value pairs. A dictionary key are usually
numbers or strings.
Dictionaries are enclosed by curly braces ( { } ) and values can be assigned and
accessed using square braces ( [] ). For example:
dict = {}
dict['one'] = "This is one"
dict[2]

= "This is two"

tinydict = {'name': 'john','code':6734, 'dept': 'sales'}

print dict['one']

# Prints value for 'one' key

print dict[2]

# Prints value for 2 key

print tinydict

# Prints complete dictionary

print tinydict.keys() # Prints all the keys
print tinydict.values() # Prints all the values
Output:
This is one
This is two
{'dept': 'sales', 'code': 6734, 'name': 'john'}
['dept', 'code', 'name']
['sales', 6734, 'john']

Operators
Simple answer can be given using expression 4 + 5 is equal to 9. Here, 4 and 5 are
called operands and + is called operator. Python language supports the following types
of operators.
➢ Arithmetic Operators
➢ Comparison (i.e., Relational) Operators
➢ Assignment Operators
➢ Logical Operators
➢ Bitwise Operators
➢ Membership Operators
➢ Identity Operators

Python Arithmetic Operator
a = 21
b = 10
C=0
c=a+b
print "Line 1 - Value of c is ", c
c=a-b
c=a*b

c=a/b
c=a%b
a=2
b=3
c = a**b
a = 10
b=5
c = a//b

Output:
Line 1 - Value of c is 31

Example:
a = 10
b = 20
list = [1, 2, 3, 4, 5 ];
if ( a in list ):
print "Line 1 - a is available in the given list"
else:
print "Line 1 - a is not available in the given list"
if ( b not in list ):
print "Line 2 - b is not available in the given list"
else:
print "Line 2 - b is available in the given list"

a=2
if ( a in list ):
print "Line 3 - a is available in the given list"
else:
print "Line 3 - a is not available in the given list"
Output:
Line 1 - a is not available in the given list
Line 2 - b is not available in the given list
Line 3 - a is available in the given list

a = 20
b = 20
if ( a is b ):
print "Line 1 - a and b have same identity"
else:
print "Line 1 - a and b do not have same identity"

b = 30
if ( a is b ):
else:

if ( a is not b ):
else:
Output:
Line 1 - a and b have same identity
Line 3 - a and b do not have same identity
Line 4 - a and b do not have same identity

Python slide.1

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Python slide.1