GE8151 Problem Solving and Python Programming

GE8151 - Problem Solving and Python Programming
Important University Questions and Answers
Prepared By
B.Muthukrishna Vinayagam, Assistant Professor/CSE

The print Statement
>>> print ('hello‘)
hello
>>> print ( 'hello', 'there‘ )
hello there
>>>a=15
>>>print(“The value of a is %d.” %(a) )
•Elements separated by commas
print with a space between them
•A comma at the end of the
statement (print ‘hello’,) will not print
a newline character
Interactive Mode Script Mode - filename.py
print (‘hello’)
Run: python filename.py
Output: hello

Variables
• Are not declared, just assigned
• The variable is created the first time you assign it
a value
• Are references to objects
• Type information is with the object, not the
reference
• Everything in Python is an object

Object Pooling
c=a
id(a)
id(b)
Id( c )

Beginners' Python 8
Built-in Object Types (Data Types)
Type Ordered Mutable Examples
Numbers N/A No 3.14, 123, 99L, 1-2j, 071, 0x0a
Strings Yes No 'A string', "A double ed string"
Lists Yes Yes [1, [2, 'three'], [5E-1, 10e3], -8L]
Dictionaries No Yes {‘key':‘value', ‘b':'ball'}
Tuples Yes No (1, 'two', -3j, 04, 0x55, 6L)
Can be changed in place?
Can be indexed/sliced?

Functions, Procedures A function is a group of
statements that together perform a task.
def name(arg1, arg2, ...):
"""documentation""" # optional doc string
statements
return # from procedure
return expression # from function

Function Basics
def max(x,y) :
if x < y :
return x
else :
return y
>>> import functionbasics
>>> max(3,5)
5
>>> max('hello', 'there')
'there'
>>> max(3, 'hello')
'hello'
functionbasics.py

Anonymous Functions
• A lambda
expression returns a
function object
• The body can only
be a simple
expression, not
complex statements
>>> f = lambda x,y : x + y
>>> f(2,3)
5
>>> lst = ['one', lambda x : x * x, 3]
>>> lst[1](4)
16

Duck Typing
• Function Overloading: achieved polymorphism
#function definition
def add(x,y,z):
return x+y+z
#function calling Output
add(10,20,30) #60
add('muthu',"krishna","vinayagam") #muthukrishnavinayagam
add(5.5,4.5,15.5) #25.5

Example Function
" " " greatest common divisor" " "
def gcd(a, b):
while a != 0:
a, b = b%a, a # parallel assignment
return b
>>> gcd.__doc__
'greatest common divisor'
>>> gcd(12, 20)
4

Required argument
def fun(a,b):
#statement
fun(10) #throws error
Keyword argument
def fun(a,b):
#statement
fun(b=10, a=”Python”)
Default argument with value
def fun(a, b=20):
#statement
fun(10)
Variable length argument
def fun(*var):
#statement
fun(10,20,30)

def foo(x, y):
global a
a = 42
x,y = y,x
b = 33
b = 17
c = 100
print(a,b,x,y)
a, b, x, y = 1, 15, 3,4 foo(17, 4)
print(a, b, x, y)
Global and Local Variable
The output looks like this:
42 17 4 17
42 15 3 4

Strings & its operation
It is collection of characters enclosed by
single/double/triple quotes
Example: 'single quotes' """triple quotes""" r"raw strings"
• "hello"+"world" "helloworld" # concatenation
• "hello"*3 "hellohellohello" # repetition
• "hello"[0] "h" # indexing
• "hello"[-1] "o" # (from end)
• "hello"[1:4] "ell" # slicing
• len("hello") 5 # size
• "hello" < "jello" 1 # comparison
• "e" in "hello" True # search
• "hello“[::-1] “olleh” #reverse
• "escapes: n etc, 033 etc, tif etc“ #display escape sequence

capitalize() Converts first character to Capital Letter
center() Pads string with specified character
count() returns occurrences of substring in string
endswith() Checks if String Ends with the Specified Suffix
encode() returns encoded string of given string
find() Returns the Highest Index of Substring
format() formats string into nicer output
index() Returns Index of Substring
isalnum() Checks Alphanumeric Character
isalpha() Checks if All Characters are Alphabets

Conditional Statements
if condition:
#stm
elif condition:
#stm
else:
#stm
if condition:
#stm
No Switch Statement:
print({1:”one”,2:”Two”,3:”Three”}.get(1,”Invalid”))
if condition:
#stm
else:
#stm

While loop
Syntax
while condition:
#stms
Example:
i=1
While i<=5:
print(i)
i=i+1
Output: 1 2 3 4 5

For Loops
• Similar to perl for loops, iterating through a list of values
~: python forloop1.py
1
7
13
2
for x in [1,7,13,2] :
print xforloop1.py
~: python forloop2.py
0
1
2
3
4
for x in range(5) :
print xforloop2.py
range(N) generates a list of numbers [0,1, …, n-1]

Loop Control Statements
break Jumps out of the closest
enclosing loop
continue Jumps to the top of the closest
enclosing loop
pass Does nothing, empty statement
placeholder

List Operations & its methods
>>> a=[1,5,10] # List creation
>>> a = range(5) # [0,1,2,3,4]
>>> a.append(5) # [0,1,2,3,4,5]
>>> a.pop() # [0,1,2,3,4]
5
>>> a.insert(0, 42) # [42,0,1,2,3,4]
>>> a.pop(0) # [0,1,2,3,4]
42
>>> a.reverse() # [4,3,2,1,0]
>>> a.sort() # [0,1,2,3,4]
>>>print(len(a)) #5

Methods Functions
append() to add element to the end of the list
extend() to extend all elements of a list to the another list
insert() to insert an element at the another index
remove() to remove an element from the list
pop() to remove elements return element at the given index
clear() to remove all elements from the list
index() to return the index of the first matched element
count() to count of number of elements passed as an argument
sort() to sort the elements in ascending order by default
reverse() to reverse order element in a list
copy() to return a copy of elements in a list

Tuples
• key = (lastname, firstname)
• point = x, y, z # parentheses optional
• x, y, z = point # unpack
• lastname = key[0]
• singleton = (1,) # trailing comma!!!
• empty = () # parentheses!

Python Expression Results Operation
len((1, 2, 3)) 3 Length
(1, 2, 3) + (4, 5, 6) (1, 2, 3, 4, 5, 6) Concatenation
('Hi!',) * 4
('Hi!', 'Hi!', 'Hi!',
'Hi!')
Repetition
3 in (1, 2, 3) True Membership
for x in (1, 2, 3): print x, 1 2 3 Iteration
Tuple and its Operations
tuple=(10,20,20,40)
len(tuple) -> Gives the total length of the tuple.
max(tuple) -> Returns item from the tuple with max value.
min(tuple) -> Returns item from the tuple with min value.
tuple(seq) -> Converts a list into tuple.
tuple1=(10,20,20,40)
tuple2=(20,20,20,40)
cmp(tuple1, tuple2) -> Compares elements of both tuples.

Dictionaries
• Hash tables, "associative arrays"
• d = {"duck": "eend", "water": "water"}
• Lookup:
• d["duck"] #eend
• d["back"] # raises KeyError exception
• Delete, insert, overwrite:
• d["back"] = "rug" # {"duck": "eend", "water": "water“,"back": "rug"}
• del d["water"] # {"duck": "eend", "back": "rug"}
• d["duck"] = "duik" # {"duck": "duik", "back": "rug"}
•Keys, values, items:
d.keys() -> ["duck", "back"]
d.values() -> ["duik", "rug"]
d.items() -> [("duck","duik"), ("back","rug")]

Dictionaries & its Operation & Methods:
len(dict) -> Gives the total length of the dictionary. This would be equal to the number of
items in the dictionary.
str(dict) -> Produces a printable string representation of a dictionary
type(variable) -> Returns the type of the passed variable. If passed variable is dictionary,
then it would return a dictionary type.
cmp(dict1, dict2) -> Compares elements of both dict.
Accessing Values in Dictionary
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
print (dict['Name'])
Updating Dictionary
dict['Age'] = 8 # update existing entry
dict['School'] = "DPS School" # Add new entry
print (dict['School'])
Delete Dictionary Elements
del dict['Name']; # remove entry with key 'Name'
dict.clear(); # remove all entries in dict
del dict ; # delete entire dictionary
Five methods are used to delete the elements from the dictionary:
pop(), popitem(), clear(), del(), update(d)

File operation:
Step1: Open a file object in read or write or append mode
Step2: Read or write the file contents using read() or write()
methods
or
Read or write entire line of file using readline() or
writelines() methods
Step3: Close file object close() method
Example
f=open("sample.txt","r")
print(f.read())
f.close()

File operation
fobj.read(7); # read only 5th bytes
fobj.tell(); #tell the current position
fobj.seek(5); #move to the 5th byte location
import os
os.rename(“old.txt”, “new.txt”)
os.remove(“file.txt”)

File Copy
1)
from shutil import copyfile
copyfile('test.py', 'abc.py')
2)
f1=open(“t.txt","r")
f2=open(“d.txt",“w")
c=f1.read()
f2.write(c)
f1.close()
f2.close()

An exception is an event, which occurs during the execution
of a program that disrupts the normal flow of the program's
instructions.
Need of Exception Handling:
• An exception is an error that happens during execution of a
program. When that error
occurs, Python generate an exception that can be handled,
which avoids your program
to crash.
• Need graceful exit that is save all works and close it.
Syntax:
try:
# Suspected Code
except:
# Remedial Action

Exception: To handle Abnormal
program termination, gracefully exit
while True:
try:
n = int(input("Please enter an integer: "))
break
except ValueError:
print("No valid integer! Please try again ...")
finally:
print("Great, you successfully entered an integer!")

def divide(x, y):
try:
result = x / y
except ZeroDivisionError:
print("division by zero!")
else:
print("result is", result)
finally:
print("executing finally clause")
Note: if try block doesn’t raise the exception then
else block is executed.
Finally block is always executed or clean up process

User Exception
class MyException(Exception):
#pass
Code snippet
while True:
try:
n = int(input("Please enter an integer: "))
raise MyException("An exception doesn't always prove the rule!")
except ValueError:
print("No valid integer! Please try again ...")
finally:
print("Great, you successfully entered an integer!")

Module: Python has a way to put definitions in a file and use them in a
script or in an interactive instance of the interpreter. Such a file is
called a module; definitions from a module can be imported into other
modules or into the main module
fibo.py
def fib1(n): # write Fibonacci series up to n
a, b = 0, 1
while b < n:
print(b, end=' ')
a, b = b, a+b
print()
def fib2(n): # return Fibonacci series up to n
result = []
a, b = 0, 1
while b < n:
result.append(b)
a, b = b, a+b
return result
>>>import fibo or >>>from fibo import fib2
>>>fibo.fib1(5) # 1 1 2 3 5

Package
New directory: demopack
• First.py
• Second.py
• __init__.py
Use Package
Test.py
from demopack import First
from demopack import Second
First.display()
Second.show()

GE8151 Problem Solving and Python Programming

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