Python tutorial¶

official website : http://www.python.org
official tutorial : http://docs.python.org/tutorial/
introduction to python programming : http://femhub.com/textbook-python/
google-style recomendations : http://google-styleguide.googlecode.com/svn/trunk/pyguide.html
a tutorial in French: http://www.siteduzero.com/informatique/tutoriels/apprenez-a-programmer-en-python

Using python with the interpreter¶

using python with the interpreter:

$ python
[GCC 4.4.4 20100503 (Red Hat 4.4.4-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

or using the more advanced interactive python interperter ipython:

$ ipython
Python 2.6.6 (r266:84292, Jan  4 2012, 16:09:28)
Type "copyright", "credits" or "license" for more information.

IPython 0.10 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object'. ?object also works, ?? prints more.

In [1]:

Simple examples:

>>> x = 1
>>> y = 2.
>>> type(x)
<type 'int'>
>>> type(y)
<type 'float'>
>>>

Operations:

>>> x+y
3.0
>>> z = x+y
>>> x==y
False
>>> x!=y
True
>>> x>y
False

Basic python objects¶

strings:

>>> name = "Meylan"
>>> name[0]
'M'
>>> name[2:4]
'yl'

dictionary:

>>> onglet={'observatoire':'obswww.unige.ch','tsr':'www.tsr.ch'}
>>> type(onglet)
<type 'dict'>
>>> onglet['observatoire']
'obswww.unige.ch'
>>> onglet['tsr']
'www.tsr.ch'
>>> onglet['epfl'] = "www.epfl.ch"
>>> onglet.keys()
['epfl', 'tsr', 'observatoire']
>>> onglet.has_key('tsr')
True

lists:

>>> trousse=['gommme', 'crayon', 'plume', 1, 1.2]
>>> type(trousse)
<type 'list'>
>>> trousse[0]
'gommme'
>>> trousse[-1]
1.2
>>> trousse.index('crayon')
1
>>> trousse.pop()
1.2
>>> trousse.pop()
1
>>> trousse.append("compas")

Control Flow Tools¶

if/else/for/while/range/xrange/break/continue/pass

if:

>>> x = 0
>>> if x==1:
...   print "x equal 1"
... else:
...   print "x is not equal to 1"
...
x is not equal to 1

for:

>>> for x in trousse:
...   print x
...
gommme
crayon
plume
compas

>>> for x in xrange(10):
...   print x
...
0
1
2
3
4
5
6
7
8
9

break:

>>> for x in xrange(10):
...   print x
...   if x==5:
...     break
...
0
1
2
3
4
5

continue:

>>> for x in xrange(10):
...   print x
...   if x==5:
...     break
...   else:
...     continue
...
0
1
2
3
4
5

while:

>>> x = 0
>>> while(x<5):
...   print x
...   x+=1
...
0
1
2
3
4

Functions¶

Define functions:

>>> def multiply(x,y):
...   z = x*y
...   return z
...
>>> multiply(2,3)
6

with optional arguments:

>>> def multiply(x,y,verbose=False):
...   if verbose:
...     print "computing x*y"
...   z = x*y
...   return z
...
>>> multiply(2,3)
6
>>> multiply(2,3,True)
computing x*y
6
>>> multiply(2,3,verbose=True)
computing x*y
6
>>>

Files¶

Open and write into a file:

>>> fd=open('fichier.txt','w')
>>> fd.write("tu vois comme c'est simple python !\n")
>>> fd.close()

Open and read a file:

>>> fd=open('fichier.txt','r')
>>> lines = fd.readlines()
>>> fd.close()
>>>
>>> print lines
["tu vois comme c'est simple python !\n"]

Miscellaneous operating system interfaces¶

>>> import os
>>> import glob
>>> import shutil

>>> os.mkdir('test')
>>> os.chdir('test')
>>> os.getcwd()

>>> open('file1','w')
>>> os.symlink('file1','file2')
>>> os.mkdir('directory')

>>> glob.glob('*')
>>> os.listdir('.')

>>> os.path.isfile('file1')
>>> os.path.isfile('file2')
>>> os.path.isfile('file3')

>>> os.path.isfile('directory')
>>> os.path.isdir('directory')

>>> os.remove('file1')
>>> os.remove('directory')
>>> os.removedirs('directory')

>>> os.chdir('../')

>>> shutil.rmtree('test')

Scripting python¶

open/create a file:
```
$ gedit myscript.py
```
add a header:
```
#!/usr/bin/env python
```

add your python commands:

#!/usr/bin/env python

print "Hello world !"

save the file
make it executable:
```
$ chmod a+x myscript.py
```
launch it !:
```
$ ./myscript.py
Hello world !
```