[Tutorial] Learning programming with Python, part V

[Acid_Snake]

Part V - Some Modules
As promised I'm going to let you guys in to some very useful modules built-in with Python.
Importing (loading) a module:
You should know this by now, but in case you don't:

Code: Select all

import name_of_the_module

You can use variables to refer to a module, but it has to be declared on module load:

Code: Select all

import this_module as this_var

I will only explain some basic and useful parts for some modules, not everything. For more help on modules, use:

Code: Select all

import whatever_module
help(whatever_module)

os:
The os module provides a set of OS-based commands, mostly file operations (remove, copy, chown, chmod....). Some examples:
Change directory:

Code: Select all

os.chdir(path)

so to navigate to the root:

Code: Select all

os.chdir("/")   # in Linux
os.chdir("c:\")   # in Windows

Change access permission:

Code: Select all

os.chmod(path, mode)
# path must be a string, mode must be an integer

Change owner/group

Code: Select all

os.chown(path, uid, gid)

There are many more, but more interesting is os.system(). os.system is used to pass commands to the system:

Code: Select all

os.system("uname -a")
os.system("ls -a")
os.system("sudo apt-get install ubuntu-desktop")
os.system("vlc")

if the commands are executed and exited correctly it will return a 0, any other number means an error:

Code: Select all

if os.system("apt-get -v") != 0:
  print "You don't have apt-get installed"
elif os.system("apt-get -v") == 0:
  print "You have apt-get installed"

random:
The random module is used to do things that involve random choices or generators, it can be used to create random numbers/strings or randomly select from a list.
Select from a list:

Code: Select all

x = [1,2,3,4,5,6,7,8,9,0]
random.choice(x)

Generate a random number:

Code: Select all

int("".join(random.sample("1234567890",10)))

10 is the length, so it can be any number depending on the number of integers you want.
Generate a random string:

Code: Select all

"".join(random.sample("qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890",10))

Generate a random number within a range:

Code: Select all

random.randrange(10)

This will generate a number from 0 to 10.

zipfile:
A module for loading, extracting and creating .zip files.
Creating a file:

Code: Select all

zipf = zipfile.ZipFile(path_to_file, "w")

Opening a zip file:

Code: Select all

zipf = zipfile.ZipFile(path_to_file, "r")

Adding a file to the zip file:

Code: Select all

x = "name of the file to be stored"
zipf.writestr(x, open(x, "rb").read())

Extracting everything:

Code: Select all

y = "Path to extract everything"
zipf.extractall(y)

Note: extractall() is available from python 2.6 and up
Example:
We're going to create a file named test.txt, write something to that file, store it in a zip file named test.zip and extract it in a folder test:

Code: Select all

import os, zipfile
x = open("test.txt","w")
x.write("test")
x.close()
zipf = zipfile.ZipFile("test.zip", "w")
zipf.writestr("test.txt", open("test.txt", "rb").read())
os.mkdir("test")
zipf.extractall("test")

urllib2:
Mostly a module for conecting to a URL, it can be used to download a file:

Code: Select all

url = "www.some.url.of.a.file.com"
dl = urllib2.urlopen(url)
dl_file = open("whatever_file","w")
dl_file.write(dl.read())
dl_file.close()

shutil:
A very little used yet powerful module, it provides a wrapper for some os functions to work on files an folders, some functions:
shutil.copyfile(source, destiny) --> copy a file from source to destiny
shutil.copytree(source, destiny) --> recursively copy a folder from source to destiny
shutil.move(source, destiny) --> recursively move a directory/file from source to destiny
shutil.rmtree(directory) --> (recursively) remove a directory

sys:
This module includes functions that interact with the Python interpreter itself, normally you don't need to use it, except the function sys.exit() which will terminate your app:

Code: Select all

sys.exit("exiting...")

Tkinter:
Tkinter is the default GUI toolkit with Python, it doesn't have much in terms of widgets, but it can be useful for quick and simple GUIs. I will explain this module more in-depth later.

That's all for now.

Previous: viewtopic.php?f=37&t=11904
Next: viewtopic.php?f=37&t=13056

[qwikrazor87]

Good job with the tutorials.
I hope you have time to make more. I'm thinking about getting into Python, it has some interesting functions that I could make use of. Thanks.

[Acid_Snake]

I just made a tutorial for GUI programming with Tkinter, you can find it here: viewtopic.php?f=37&t=13056
If you are looking for something more specific just ask me and I might add it to the tutorials.

[qwikrazor87]

Thank you. It'd be awesome if you made tutorials aimed toward coding for the PSP.

[Acid_Snake]

Thank you. It'd be awesome if you made tutorials aimed toward coding for the PSP.

I had that in mind too! I'll use example codes from some of my homebrews.

[qwikrazor87]

Thanks a lot. I'll be looking forward to it.