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Agenda
Advanced Python Tutorial

Agenda
Introduction 01
Introduction to
Advanced Python
Getting Started 02
Concepts 03
Practical Approach 04
Python and Shell
Looking at code to
understand theory
Key Concepts in Python

Introduction to Advanced Python

Introduction To Advanced Python
Python is an interpreted, high-level, general-purpose
programming language.
What is Python?
Advanced: Other
Languages
Learning
Advanced Python

What Is Advanced Python
Computer Science5
Numerical Compute6
Databases7
Sys Programming 1
Graph Theory 2
Mathematics 3
Python spreading its wings across multiple dimensions and
use-cases in many fields
What is “Advanced”?

Introduction To System Programming

System Programming
Sys - Module
Hello Advanced Python!
Import sys
Provides information about constants, functions
and methods of the Python interpreter.
Data streams
stdout stderrstdin
>>> import sys
>>> sys.version
'2.6.5 (r265:79063, Apr 16 2010,
13:57:41) n[GCC 4.4.3]'
>>> sys.version_info
(2, 6, 5, 'final', 0)
>>>

Command – Line Arguments
Sys - Module
Command Line
argcargv
#!/usr/bin/python
import sys
# it's easy to print this list of course:
print sys.argv
# or it can be iterated via a for loop:
for i in range(len(sys.argv)):
if i == 0:
print "Function name: %s" % sys.argv[0]
else:
print "%d. argument: %s" % (i,sys.argv[i])
$ python arguments.py arg1 arg2
['arguments.py', 'arg1', 'arg2']
Function name: arguments.py
1. argument: arg1
2. argument: arg2
$

Changing Output Behaviour
Sys - Module
Python
Interactive Mode
Get Output
Write expression
>>> import sys
>>> x = 42
>>> x
42
>>> import sys
>>> def my_display(x):
... print "out: ",
... print x
...
>>> sys.displayhook = my_display
>>> x
out: 42
>>>
>>> print x
42
Behaviour of print() not changed

Standard Data Streams
Sys - Module
>>> import sys
>>> for i in (sys.stdin, sys.stdout, sys.stderr):
... print(i)
...
', mode 'w' at 0x7f3397a2c150>
', mode 'w' at 0x7f3397a2c1e0>
>>>
SHELLstdin stdout
stderr
>>> import sys
>>> print "Going via stdout"
Going via stdout
>>> sys.stdout.write("Another way to do it!n")
Another way to do it!
>>> x = raw_input("read value via stdin: ")
read value via stdin: 42
>>> print x
42
>>> print "type in value: ", ; sys.stdin.readline()[:-1]
type in value: 42
'42'
>>>

Redirections
Sys - Module
import sys
print("Coming through stdout")
# stdout is saved
save_stdout = sys.stdout
fh = open("test.txt","w")
sys.stdout = fh
print("This line goes to test.txt")
# return to normal:
sys.stdout = save_stdout
fh.close()
SHELLstdin stdout
stderr
import sys
save_stderr = sys.stderr
fh = open("errors.txt","w")
sys.stderr = fh
x = 10 / 0
# return to normal:
sys.stderr = save_stderr
fh.close()

Variables & Constants In Sys Module
Sys - Module
byteorder
executable
maxint
modules
path
platform
Variables Constants

Python And Shell

Python And Shell
A piece of software that provides an interface for a user to some
other software or the operating system
What is “Shell”?
SHELL
GUICUI
Bourne-Shell
C-Shell
Bash Shell

System Programming
The activity of programming system components or system
software
What is “SP”?
“System focussed programming”
Modules
sys os
Simple and clear
Well structured
Highly flexible
Advantages

The ‘os’ Module
The os module allows platform independent programming by
providing abstract methods
What is “os” module?
Executing Shell scripts with os.system()
import os
def getch():
os.system("bash -c "read -n 1"")
getch()
from msvcrt import getch

The ‘os’ Module
Executing Shell scripts with os.system()
import os, platform
if platform.system() == "Windows":
import msvcrt
def getch():
if platform.system() == "Linux":
os.system("bash -c "read -n
1"")
else:
msvcrt.getch()
print("Type a key!")
getch()
print("Okay")
Subprocess Module
os.system
os.spawn*
os.popen*

Forking In Python

Fork In Python
What is Forking?
import os
def child():
print('nA new child ', os.getpid())
os._exit(0)
def parent():
while True:
newpid = os.fork()
if newpid == 0:
child()
else:
pids = (os.getpid(), newpid)
print("parent: %d, child: %dn"
% pids)
reply = input("q for quit / c for
new fork")
if reply == 'c':
continue
else:
break
parent()
Process
Copy of Process
Parent
Child
Starting independent processes with fork()
exec*() function

The exec*() Functions
exec*() functions
• os.execl(path, arg0, arg1, ...)
• os.execle(path, arg0, arg1, ..., env)
• os.execlp(file, arg0, arg1, ...)
• os.execlpe(file, arg0, arg1, ..., env)
• os.execv(path, args)
• os.execve(path, args, env)
• os.execvp(file, args)
• os.execvpe(file, args, env)

Threads In Python

What Is A Thread?
The smallest unit that can be scheduled in an operating systemWhat is a thread?
How to create a thread?
By forking a computer program in
two or more parallel tasks
Types of threads
Kernel threads User threads
Implemented in kernel NOT implemented in kernel

What Is A Thread?
Global Variables
Process
Local variables
Code
THREAD
Local variables
Code
THREAD
Local variables
Code
THREAD

The Thread Module
from thread import start_new_thread
def heron(a):
"""Calculates the square root of a"""
eps = 0.0000001
old = 1
new = 1
while True:
old,new = new, (new + a/new) / 2.0
print old, new
if abs(new - old) < eps:
break
return new
start_new_thread(heron,(99,))
c = raw_input("Type something to quit.")
Example

The Thread Module
from thread import start_new_thread
num_threads = 0
def heron(a):
global num_threads
num_threads += 1
# code has been left out, see above
num_threads -= 1
return new
while num_threads > 0:
pass
Previous example with counters for the threads
• Reading the value of num_thread
• A new int instance will be incremented or
decremented by 1
• the new value has to be assigned to
num_threads

The Thread Module
from thread import start_new_thread, allocate_lock
num_threads = 0
thread_started = False
lock = allocate_lock()
def heron(a):
global num_threads, thread_started
lock.acquire()
num_threads += 1
thread_started = True
lock.release()
...
lock.acquire()
num_threads -= 1
lock.release()
return new
while not thread_started:
pass
while num_threads > 0:
pass
The solution

Threading Module
import time
from threading import Thread
def sleeper(i):
print "thread %d sleeps for 5 seconds" % i
time.sleep(5)
print "thread %d woke up" % i
for i in range(10):
t = Thread(target=sleeper, args=(i,))
t.start()
Example
The Thread of the example doesn't do a lot, essentially it just
sleeps for 5 seconds and then prints out a message:

Threading Module
thread 0 sleeps for 5 seconds
thread 1 woke up
thread 0 woke up
thread 3 woke up
thread 2 woke up
thread 5 woke up
thread 9 woke up
thread 8 woke up
thread 7 woke up
thread 6 woke up
thread 4 woke up

Pipes In Python

What Are Pipes
Introducing modularity in the program to serve one instance output as
the input to another instance and so on till solution is achieved
What are pipes?
Two kinds of pipes
Named PipesAnonymous Pipes
Exist solely within processes and are usually
used in combination with forks
P1
P2
P3
P4

Pipes – A Classic Example
99 Bottles of Beer
Drinking is injurious to health
Ninety-nine bottles of beer on the wall, Ninety-nine bottles of beer.
Take one down, pass it around, Ninety-eight bottles of beer on the wall.
Lyrics of the song:

Named Pipes
Called FIFOs – Creating pipes which are implemented as files.What are named pipes?
First In – First Out
A process reads from and writes to such a pipe as if it
were a regular file. Sometimes more than one process
write to such a pipe but only one process reads from it.

Conclusion

Conclusion
Advanced Python, yay!

Advanced Python Tutorial | Learn Advanced Python Concepts | Python Programming Training | Edureka

Advanced Python Tutorial | Learn Advanced Python Concepts | Python Programming Training | Edureka

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