Python

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Python

October 18, 2017 Uncategorized 0 
Exercises at -

Python Exercise 1


Python Exercise 2


Python Exercise 3



----> hello.py
import re

def foo():
    print("Hello Amar Sharma")

if __name__ == "__main__":
 foo()

TRY FROM REPL

Strings examples

 >>> name1 = "John"
 >>> name2 = "Doe"
 >>> "My name is %s " % name1
 'My name is John '
 >>> name1 + " " + name2
 'John Doe'
 >>> if "J" in name1:
         print("Yes, J's there")
    
Yes, J's there

Strings examples

>>> for i in name1:
    print(i)
J
o
h
n
>>>name1.replace("h","a")
'Joan'
>>> name1
'John'

Strings examples

>>>name1.find("hn")
2
>>> list(name1)
['J', 'o', 'h', 'n']
>>> name1*4
'JohnJohnJohnJohn'
>>> foo = "Python:Perl:Ruby:TCL:Shell"
>>> foo.split(":")
['Python', 'Perl', 'Ruby', 'TCL','Shell']

List examples

>>> foo = ["J","o","h","n"]
>>> foo
['J', 'o', 'h', 'n']
>>> foo.append(" ")
>>> foo
['J', 'o', 'h', 'n', ' ']
>>> foo.extend(["D","o","e"])
>>> foo
['J', 'o', 'h', 'n', ' ', 'D', 'o', 'e']
>>> "".join(foo)
'John Doe'
>>> " ".join(foo)
'J o h n D o e'
>>> foo.reverse()
>>> foo

['e', 'o', 'D', ' ', 'n', 'h', 'o', 'J']

>>> foo = ["J","o","h","n"]
>>> for i in foo:
     print(foo.index(i),i)
    
0 J
1 o
2 h
3 n
>>> foo
['J', 'o', 'h', 'n']
>>> foo[2]
'h'
>>> foo[2]="a"
>>> foo
['J', 'o', 'a', 'n']
>>> foo.sort()
>>> foo
['J', 'a', 'n', 'o']
>>> foo.pop()
'o'
>>> foo.pop()
'n'
>>> foo.pop()
'a'
>>> foo.pop()
'J'
>>> foo
[]

>>> foo = "This is the last time I'm going to say this".split()
>>> foo
['This', 'is', 'the', 'last', 'time', "I'm", 'going', 'to', 'say', 'this']
>>> foo[2]
'the'
>>> foo[2:6]
['the', 'last', 'time', "I'm"]
>>> foo[-2]
'say'
>>> foo[:-2]
['This', 'is', 'the', 'last', 'time', "I'm", 'going', 'to']
>>> foo[4:]
['time', "I'm", 'going', 'to', 'say', 'this']
>>>

Dictionary examples

>>> os = { "Microsoft" : "Windows",
    "Sun" : "Solaris",
    "Belllabs" : "Plan 9",
    "SGI" : "Irix"}

 >>>
 >>> os
 {'Bell labs': 'Plan 9', 'Sun': 'Solaris', 'SGI': 'Irix', 'Microsoft': 'Windows'}

for i in os.keys():
    print(i,os[i])
    
 Bell labs Plan 9
 Sun Solaris
 SGI Irix
 Microsoft Windows
 >>>
 >>> os.has_key("Apple")
 False
 >>> "Apple" in os
 False
 >>> "Sun" in os
 True
 >>> os.values()
 ['Plan 9', 'Solaris', 'Irix', 'Windows']
 >>> os.keys()
 ['Bell labs', 'Sun', 'SGI', 'Microsoft']
 >>> os2 = {"FSF": "Gnu/Linux","Apple" : "OSX"}
 >>> os2
 {'Apple': 'OSX', 'FSF': 'Gnu/Linux'}
 >>> os.update(os2)
 >>> for i in os.keys():
         #print(i,":",end='')
         print(i,":"),
 Bell labs : SGI : Apple : FSF : Sun : Microsoft : >>>

Tuples

>>> tuple("Python")
('P', 'y', 't', 'h', 'o', 'n')
>>> foo = (1,2,3)
>>> foo[1] = 7
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> foo = (1,)
>>> type(foo)
<type 'tuple'>
>>>

Files

>>> foo = open("/home/mohan/ip.php")
>>> foo.read(20)
'<?php\necho $_SERVER['
>>> foo.readline()
"'REMOTE_ADDR'];\n"
>>> foo.readline()
 '\n'
>>> foo.readline()
'$url = json_decode(file_get_contents("http://api.ipinfodb.com/v3/ip-city/? key=<your_api_key>&ip=".$_SERVER[\'REMOTE_ADDR\']."&format=json"));\n'
>>> x=foo.readlines()
>>> len(x)
 23
>>> x[4]
 'echo "<table border=\'1\' width=\'50%\' align=\'center\'><tr><td>COUNTRY:</td><td>";\n'
>>> foo.close()
>>> foo.read()
 Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 ValueError: I/O operation on closed file
>>>

Idea of python objects

  • >>> foo = “Wozniak”
>>> bar = foo
>>> id(foo)
139807526833968
>>> id(bar)
139807526833968
>>> baz = "Wozniak"
>>> id(baz)
139807526833968
>>>
>>> foo = range(1,100)
>>> bar = range(1,100)
>>> id(foo)
139807526796536
>>> id(bar)
139807526796320
>>> foo is bar
False
>>> foo == bar
True
>>>

Assignments

>>> foo = ("Wozniak","Apple","Designer")
>>> name,company,position = foo
>>> name
'Wozniak'
>>> position
'Designer'
>>> foo,bar = 1,2
>>> foo,bar = bar,foo
>>> foo
2
>>> bar
1
>>>
  • Multiple targets
>>> a=b=1
>>> a
1
>>> b
1
>>>
  • Augmented assignments
>>> foo=1
>>> foo+=1
>>> foo
 2
>>>

Conditional Branching statements

  • If statements 
    >>> foo = 11
>>> if foo < 9:
    print("Less than nine")
elif foo > 10:
    print("Greater than 10")
else:
    print("Between 9 and 10")
 
Greater than 10
  • Multiway branching with dictionaries
>>> choice = "eggs"
>>> print ({"spam" : 10,"eggs" : 20,"veg" : 15}[choice])
20
>>>

Indefinite iteration

>>> while 1:
     x = next()
     if not x: break
     print(x)

Definite iteration

>>> for i in range(1,10):
     #print (i,":",end='')
     print(i,":"),
1 : 2 : 3 : 4 : 5 : 6 : 7 : 8 : 9 :

Zip Function

>>> l1 = [1,3,5,7,9]
>>> l2 = [2,4,6,8,10]
>>> for (x,y) in zip(l1,l2):
     #print ("(%d,%d) : " % (x,y),end='')
     print ("(%d,%d) : " % (x,y)),
(1,2) : (3,4) : (5,6) : (7,8) : (9,10) : >>>

Example Function

>>> def thrice(arg):return arg*3
>>> thrice(4)
12
>>> thrice([1,2,3])
[1, 2, 3, 1, 2, 3, 1, 2, 3]
>>> thrice("Ni!")
'Ni!Ni!Ni!'
>>>

Functions

>>> foo = thrice
>>> foo(4)
12

Ref or Value ?

>>> bar = [1,2,3,4,5]
>>> foo(bar)
>>> bar
[1, 2, 1, 4, 5]
>>> bar = [1,2,3,4,5]
>>> foo(bar[:]) #Passing a copy
>>> bar
[1, 2, 3, 4, 5]
>>>
  • Arguments by name
>>> def fn(name,company,designation):
     print("%s works at %s as an %s" % (name,company,designation))
    
>>> fn("Noufal","Synopsys","Engineer")
Noufal works at Synopsys as an Engineer
>>> fn(company = "Synopsys",name = "Noufal",designation="Engineer")
Noufal works at Synopsys as an Engineer
>>>
  • Default arguments
>>> def fn(name,age=25):
     print("%s is %d years old" % (name,age))
    
>>> fn("John")
John is 25 years old
>>> fn("John",30)
John is 30 years old
>>>
  • Variable argument lengths by position
>>> def fn(*foo):
    for i in foo:
        #print(i,end='')
        print(i),
>>> fn(1,2,3,4,5,6,7) 1 2 3 4 5 6 7 >>>
  • Variable argument lengths by keyword
>>> def fn(**foo):
     for i in foo.keys():
        print(i,":",foo[i])
    
 >>> fn(name="John",age="50")
 age : 50
 name : John
 >>>

Modules

>>> import display
>>> display.fn("John",40)
John is 40 years old

>>> from display import *
>>> fn("John",40)
John is 40 years old

>>> from display import fn
>>> fn("John",40)
John is 40 years old
  • Module concepts
>>> mod = __import__("display")
>>> mod.fn("John",50)
John is 50 years old
  • Some standard modules
>>> import os
>>> foo = os.popen("/bin/ls")
>>> foo
<open file '/bin/ls', mode 'r' at 0x127860>
>>> op = foo.read()
>>> op
'#.bbdb#\n#.newsrc-dribble#\nMail\nNews\nStarOffice52\naudio   '
>>> files = op.split()
>>> for i in files:
        print(i)
    
 #.bbdb#
 #.newsrc-dribble#
 Mail
 News

>>> import sre
>>> numerical = sre.compile(“[0-9]+”)
>>> sstring = “Apple PowerBook for just 66000”
>>> foo = numerical.search(sstring)
>>> foo
<_sre.SRE_Match object at 0x1a16e8>
>>> foo.group()
‘66000‘
>>>

>>> import pickle
>>> spam = {"Wall" : "Perl", "Guido" : "Python", "Matsumoto" : "Ruby"}
>>> spam.keys()
['Wall', 'Matsumoto', 'Guido']
>>> foo = open("/u/noufal/ldict.pkl","w")
>>> pickle.dump(spam,foo)
>>> foo.close()
>>> del(spam)
>>> foo = open("/u/noufal/ldict.pkl","r")
>>> ham = pickle.load(foo)
>>> ham
{'Wall': 'Perl', 'Matsumoto': 'Ruby', 'Guido': 'Python'}

Classes and OOP

  • Classes behaviour
>>> class FirstClass:
     def setdata(self,value):
        self.data = value
     def display(self):
        print(self.data)
    
 >>> x = FirstClass()
 >>> y = FirstClass()
 >>> x.setdata("Eric Idle")
 >>> x.display()
 Eric Idle
 >>> dir(x)
 ['__doc__', '__module__', 'data', 'display', 'setdata']
 >>>
  • Inheritance
>>> class SecondClass(FirstClass):
     def display(self):
        print("Current value is %s" % str(self.data))
    
>>> x = SecondClass()
>>> x.setdata("King Arthur")
>>> x.display()
Current value is King Arthur
>>> class ThirdClass(SecondClass):
     def __init__(self,value):
        self.data = value
     def __add__(self,other):
        return ThirdClass(self.data + other)
    
>>> a = ThirdClass("abc")
>>> a.display()
Current value is abc
>>> b = a + "123"
>>> b.display()
Current value is abc123
>>>
  • Classes odds and ends
>>> getattr(b,"data")
'abc123'
>>> setattr(b,"data","xzy")
>>> b.data
'xzy'
>>> b.display()
Current value is xzy
  • Exceptions
>>> foo = [1,2,3,4,5]
>>> foo[10]
Traceback (most recent call last):
 File "<stdin>", line 1, in ?
IndexError: list index out of range
>>> try:
     foo[10]
     except IndexError:
          print("Index too large.")
    
 Index too large.
  • Raising your own exceptions
>>> foo = "FunError"
>>> raise foo
Traceback (most recent call last):
 File "<stdin>", line 1, in ?
FunError
>>> raise foo,"This is what you get for erroring out"
Traceback (most recent call last):
 File "<stdin>", line 1, in ?
FunError: This is what you get for erroring out
  • Documenting code
>>> def fn(name,age=30):
    "Displays persons name and age. Age defaults to 30."
    print("%s is %d years old" % (name,age))
    
>>> fn("John")
John is 30 years old
>>> print fn.__doc__
Displays persons name and age. Age defaults to 30.
  • Functional programming primitives
>>> foo = lambda x:x*3
>>> foo(2)
6

>>> apply (lambda x:x*100,(2,))
200

>>> foo = [1,2,3,4,5,6,7]
>>> map(lambda x:x*2,foo)
[2, 4, 6, 8, 10, 12, 14]
  • Functional programming continued
>>> filter (lambda x:x%2==0,range(20))
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
reduce: Apply function on sequence elements pairwise
>>> reduce(lambda x,y:x+y,range(10))
45
>>> foo = 0
>>> for i in range(10):
     foo += i
    
>>> print(foo)
45

>>> def create_incrementer(inc):
     return lambda x:x+inc
    
>>> inc3=create_incrementer(3)
>>> inc3(10)
13
  • List comprehensions
>>> [x*2 for x in range(1,10)]
[2, 4, 6, 8, 10, 12, 14, 16, 18]
>>> [x**2 for x in range(1,10) if x%2 == 0]
[4, 16, 36, 64]
>>> [(x,x**2) for x in range(1,10) if x%2 == 0]
[(2, 4), (4, 16), (6, 36), (8, 64)]
  • Generator functions
>>> def gensq(n):
     for i in range(n):
          yield i ** 2
    
>>> for i in gensq(5):
     #print(i,":",end='')
     print(i),
0 : 1 : 4 : 9 : 16 : >>> x = gensq(10) >>> x <generator object at 0x191da0> >>> x.next() 0 >>> x.next() 1 >>> x.next() 4
  • Useful development stuff
>>> import rlcompleter, readline
>>> readline.parse_and_bind('tab: complete')
>>> foo = "hello"
>>> foo.<TAB><TAB>
foo.__add__ foo.__lt__ foo.encode foo.replace
foo.__class__ foo.__mod__ foo.endswith foo.rfind
foo.__contains__ foo.__mul__ foo.expandtabs foo.rindex
foo.__delattr__ foo.__ne__ foo.find foo.rjust
foo.__doc__ foo.__new__ foo.index foo.rstrip
foo.__eq__ foo.__reduce__ foo.isalnum foo.split
foo.__ge__ foo.__reduce_ex__ foo.isalpha foo.splitlines
foo.__getattribute__ foo.__repr__ foo.isdigit foo.startswith
foo.__getitem__ foo.__rmod__ foo.islower foo.strip
foo.__getnewargs__ foo.__rmul__ foo.isspace foo.swapcase
foo.__getslice__ foo.__setattr__ foo.istitle foo.title
foo.__gt__ foo.__str__ foo.isupper foo.translat
foo.__hash__ foo.capitalize foo.join foo.upper
foo.__init__ foo.center foo.ljust foo.zfill
foo.__le__ foo.count foo.lower
foo.__len__ foo.decode foo.lstrip
  • Python DataBase Example
#!/usr/bin/python

import MySQLdb

#Open database connection
db = MySQLdb.connect("","","","information_schema" )

#prepare a cursor object using cursor() method
cursor = db.cursor()

#execute SQL query using execute() method.
cursor.execute("SELECT VERSION()")

#Fetch a single row using fetchone() method.
data = cursor.fetchone()
print "Database version : %s " % data

#disconnect from server
db.close()
  • python sample program
import MySQLdb
# Open database connection
db = MySQLdb.connect("","","","information_schema" )
# prepare a cursor object using cursor() method
cursor = db.cursor()
sql = "SELECT * FROM TABLES "
try:
 # Execute the SQL command
 cursor.execute(sql)
 # Fetch all the rows in a list of lists.
 results = cursor.fetchall()
 for row in results:
   print row
except:
 print "Error: unable to fecth data"
# disconnect from server
 db.close()

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