Le langage Python

>>> L = ['red', 'blue', 'green', 'black', 'white']
>>> type(L)
<type 'list'>

>>> L[2]
'green'

>>> L[-1]
'white'
>>> L[-2]
'black'

>>> L
['red', 'blue', 'green', 'black', 'white']
>>> L[2:4]
['green', 'black']

>>> L
['red', 'blue', 'green', 'black', 'white']
>>> L[3:]
['black', 'white']
>>> L[:3]
['red', 'blue', 'green']
>>> L[::2]
['red', 'green', 'white']

>>> L[0] = 'yellow'
>>> L
['yellow', 'blue', 'green', 'black', 'white']
>>> L[2:4] = ['gray', 'purple']
>>> L
['yellow', 'blue', 'gray', 'purple', 'white']

>>> L = ['red', 'blue', 'green', 'black', 'white']
>>> L.append('pink')
>>> L
['red', 'blue', 'green', 'black', 'white', 'pink']
>>> L.pop() # removes and returns the last item
'pink'
>>> L
['red', 'blue', 'green', 'black', 'white']
>>> L.extend(['pink', 'purple']) # extend L, in-place
>>> L
['red', 'blue', 'green', 'black', 'white', 'pink', 'purple']
>>> L = L[:-2]
>>> L
['red', 'blue', 'green', 'black', 'white']

>>> r = L[::-1]
>>> r
['white', 'black', 'green', 'blue', 'red']
>>> r2 = list(L)
>>> r2
['red', 'blue', 'green', 'black', 'white']
>>> r2.reverse() # in-place
>>> r2
['white', 'black', 'green', 'blue', 'red']

>>> r + L
['white', 'black', 'green', 'blue', 'red', 'red', 'blue', 'green', 'black', 'white']
>>> r * 2
['white', 'black', 'green', 'blue', 'red', 'white', 'black', 'green', 'blue', 'red']

>>> sorted(r) # new object
['black', 'blue', 'green', 'red', 'white']
>>> r
['white', 'black', 'green', 'blue', 'red']
>>> r.sort()  # in-place
>>> r
['black', 'blue', 'green', 'red', 'white']

s = 'Hello, how are you?'
s = "Hi, what's up"
s = '''Hello,                 # tripling the quotes allows the
       how are you'''         # the string to span more than one line
s = """Hi,
what's up?"""

In [1]: 'Hi, what's up?'
------------------------------------------------------------
   File "<ipython console>", line 1
    'Hi, what's up?'
           ^
SyntaxError: invalid syntax

>>> a = "hello"
>>> a[0]
'h'
>>> a[1]
'e'
>>> a[-1]
'o'

>>> a = "hello, world!"
>>> a[3:6] # 3rd to 6th (excluded) elements: elements 3, 4, 5
'lo,'
>>> a[2:10:2] # Syntax: a[start:stop:step]
'lo o'
>>> a[::3] # every three characters, from beginning to end
'hl r!'

In [53]: a = "hello, world!"
In [54]: a[2] = 'z'
---------------------------------------------------------------------------
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

In [55]: a.replace('l', 'z', 1)
Out[55]: 'hezlo, world!'
In [56]: a.replace('l', 'z')
Out[56]: 'hezzo, worzd!'

>>> 'An integer: %i; a float: %f; another string: %s' % (1, 0.1, 'string')
'An integer: 1; a float: 0.100000; another string: string'

>>> i = 102
>>> filename = 'processing_of_dataset_%d.txt' % i
>>> filename
'processing_of_dataset_102.txt'

>>> tel = {'emmanuelle': 5752, 'sebastian': 5578}
>>> tel['francis'] = 5915
>>> tel
{'sebastian': 5578, 'francis': 5915, 'emmanuelle': 5752}
>>> tel['sebastian']
5578
>>> tel.keys()
['sebastian', 'francis', 'emmanuelle']
>>> tel.values()
[5578, 5915, 5752]
>>> 'francis' in tel
True

>>> d = {'a':1, 'b':2, 3:'hello'}
>>> d
{'a': 1, 3: 'hello', 'b': 2}

>>> t = 12345, 54321, 'hello!'
>>> t[0]
12345
>>> t
(12345, 54321, 'hello!')
>>> u = (0, 2)

>>> s = set(('a', 'b', 'c', 'a'))
>>> s
set(['a', 'c', 'b'])
>>> s.difference(('a', 'b'))
set(['c'])

In [1]: a = [1, 2, 3]
In [2]: b = a
In [3]: a
Out[3]: [1, 2, 3]
In [4]: b
Out[4]: [1, 2, 3]
In [5]: a is b
Out[5]: True
In [6]: b[1] = 'hi!'
In [7]: a
Out[7]: [1, 'hi!', 3]

In [1]: a = [1, 2, 3]
In [3]: a
Out[3]: [1, 2, 3]
In [4]: a = ['a', 'b', 'c'] # Creates another object.
In [5]: a
Out[5]: ['a', 'b', 'c']
In [6]: id(a)
Out[6]: 138641676
In [7]: a[:] = [1, 2, 3] # Modifies object in place.
In [8]: a
Out[8]: [1, 2, 3]
In [9]: id(a)
Out[9]: 138641676 # Same as in Out[6], yours will differ...

>>> vowels = 'aeiouy'

>>> for i in 'powerful':
...     if i in vowels:
...         print(i),
o e u

>>> message = "Hello how are you?"
>>> message.split() # returns a list
['Hello', 'how', 'are', 'you?']
>>> for word in message.split():
...     print word
...
Hello
how
are
you?

>>> words = ('cool', 'powerful', 'readable')
>>> for i in range(0, len(words)):
...     print i, words[i]
0 cool
1 powerful
2 readable

>>> for index, item in enumerate(words):
...     print index, item
0 cool
1 powerful
2 readable

>>> d = {'a': 1, 'b':1.2, 'c':1j}

>>> for key, val in d.iteritems():
...     print('Key: %s has value: %s' % (key, val))
Key: a has value: 1
Key: c has value: 1j
Key: b has value: 1.2

In [4]: demo?
Type:               module
Base Class: <type 'module'>
String Form:        <module 'demo' from 'demo.py'>
Namespace:  Interactive
File:               /home/varoquau/Projects/Python_talks/scipy_2009_tutorial/source/demo.py
Docstring:
    A demo module.


In [5]: who
demo

In [6]: whos
Variable   Type      Data/Info
------------------------------
demo       module    <module 'demo' from 'demo.py'>

In [7]: dir(demo)
Out[7]:
['__builtins__',
'__doc__',
'__file__',
'__name__',
'__package__',
'c',
'd',
'print_a',
'print_b']


In [8]: demo.
demo.__builtins__      demo.__init__          demo.__str__
demo.__class__         demo.__name__          demo.__subclasshook__
demo.__delattr__       demo.__new__           demo.c
demo.__dict__          demo.__package__       demo.d
demo.__doc__           demo.__reduce__        demo.print_a
demo.__file__          demo.__reduce_ex__     demo.print_b
demo.__format__        demo.__repr__          demo.py
demo.__getattribute__  demo.__setattr__       demo.pyc
demo.__hash__          demo.__sizeof__

In [9]: from demo import print_a, print_b

In [10]: whos
Variable   Type        Data/Info
--------------------------------
demo       module      <module 'demo' from 'demo.py'>
print_a    function    <function print_a at 0xb7421534>
print_b    function    <function print_b at 0xb74214c4>

In [11]: print_a()
a

In [1]: import sys

In [2]: sys.path
Out[2]:
['',
 '/home/varoquau/.local/bin',
 '/usr/lib/python2.7',
 '/home/varoquau/.local/lib/python2.7/site-packages',
 '/usr/lib/python2.7/dist-packages',
 '/usr/local/lib/python2.7/dist-packages',
 ...]

export PYTHONPATH=$PYTHONPATH:/home/emma/user_defined_modules

import sys
new_path = '/home/emma/user_defined_modules'
if new_path not in sys.path:
    sys.path.append(new_path)

In [17]: os.getcwd()
Out[17]: '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source'

In [31]: os.listdir(os.curdir)
Out[31]:
['.index.rst.swo',
 '.python_language.rst.swp',
 '.view_array.py.swp',
 '_static',
 '_templates',
 'basic_types.rst',
 'conf.py',
 'control_flow.rst',
 'debugging.rst',
 ...

In [32]: os.mkdir('junkdir')

In [33]: 'junkdir' in os.listdir(os.curdir)
Out[33]: True

In [36]: os.rename('junkdir', 'foodir')

In [37]: 'junkdir' in os.listdir(os.curdir)
Out[37]: False

In [38]: 'foodir' in os.listdir(os.curdir)
Out[38]: True

In [41]: os.rmdir('foodir')

In [42]: 'foodir' in os.listdir(os.curdir)
Out[42]: False

In [44]: fp = open('junk.txt', 'w')

In [45]: fp.close()

In [46]: 'junk.txt' in os.listdir(os.curdir)
Out[46]: True

In [47]: os.remove('junk.txt')

In [48]: 'junk.txt' in os.listdir(os.curdir)
Out[48]: False

In [70]: fp = open('junk.txt', 'w')

In [71]: fp.close()

In [72]: a = os.path.abspath('junk.txt')

In [73]: a
Out[73]: '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/junk.txt'

In [74]: os.path.split(a)
Out[74]: ('/Users/cburns/src/scipy2009/scipy_2009_tutorial/source',
          'junk.txt')

In [78]: os.path.dirname(a)
Out[78]: '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source'

In [79]: os.path.basename(a)
Out[79]: 'junk.txt'

In [80]: os.path.splitext(os.path.basename(a))
Out[80]: ('junk', '.txt')

In [84]: os.path.exists('junk.txt')
Out[84]: True

In [86]: os.path.isfile('junk.txt')
Out[86]: True

In [87]: os.path.isdir('junk.txt')
Out[87]: False

In [88]: os.path.expanduser('~/local')
Out[88]: '/Users/cburns/local'

In [92]: os.path.join(os.path.expanduser('~'), 'local', 'bin')
Out[92]: '/Users/cburns/local/bin'

In [8]: os.system('ls')
basic_types.rst   demo.py          functions.rst  python_language.rst  standard_library.rst
control_flow.rst  exceptions.rst   io.rst         python-logo.png
demo2.py          first_steps.rst  oop.rst        reusing_code.rst

In [20]: import sh
In [20]: com = sh.ls()

In [21]: print com
basic_types.rst   exceptions.rst   oop.rst              standard_library.rst
control_flow.rst  first_steps.rst  python_language.rst
demo2.py          functions.rst    python-logo.png
demo.py           io.rst           reusing_code.rst

In [22]: print com.exit_code
0
In [23]: type(com)
Out[23]: sh.RunningCommand

In [10]: for dirpath, dirnames, filenames in os.walk(os.curdir):
   ....:     for fp in filenames:
   ....:         print os.path.abspath(fp)
   ....:
   ....:
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/.index.rst.swo
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/.view_array.py.swp
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/basic_types.rst
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/conf.py
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/control_flow.rst
...

In [9]: import os

In [11]: os.environ.keys()
Out[11]:
['_',
 'FSLDIR',
 'TERM_PROGRAM_VERSION',
 'FSLREMOTECALL',
 'USER',
 'HOME',
 'PATH',
 'PS1',
 'SHELL',
 'EDITOR',
 'WORKON_HOME',
 'PYTHONPATH',
 ...

In [12]: os.environ['PYTHONPATH']
Out[12]: '.:/Users/cburns/src/utils:/Users/cburns/src/nitools:
/Users/cburns/local/lib/python2.5/site-packages/:
/usr/local/lib/python2.5/site-packages/:
/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5'

In [16]: os.getenv('PYTHONPATH')
Out[16]: '.:/Users/cburns/src/utils:/Users/cburns/src/nitools:
/Users/cburns/local/lib/python2.5/site-packages/:
/usr/local/lib/python2.5/site-packages/:
/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5'

In [10]: while True:
   ....:     try:
   ....:         x = int(raw_input('Please enter a number: '))
   ....:         break
   ....:     except ValueError:
   ....:         print('That was no valid number.  Try again...')
   ....:
Please enter a number: a
That was no valid number.  Try again...
Please enter a number: 1

In [9]: x
Out[9]: 1

In [10]: try:
   ....:     x = int(raw_input('Please enter a number: '))
   ....: finally:
   ....:     print('Thank you for your input')
   ....:
   ....:
Please enter a number: a
Thank you for your input
---------------------------------------------------------------------------
ValueError: invalid literal for int() with base 10: 'a'

In [11]: def print_sorted(collection):
   ....:     try:
   ....:         collection.sort()
   ....:     except AttributeError:
   ....:         pass
   ....:     print(collection)
   ....:
   ....:

In [12]: print_sorted([1, 3, 2])
[1, 2, 3]

In [13]: print_sorted(set((1, 3, 2)))
set([1, 2, 3])

In [14]: print_sorted('132')
132

In [15]: def filter_name(name):
   ....:    try:
   ....:        name = name.encode('ascii')
   ....:    except UnicodeError, e:
   ....:        if name == 'Gaël':
   ....:            print('OK, Gaël')
   ....:        else:
   ....:            raise e
   ....:    return name
   ....:

In [16]: filter_name('Gaël')
OK, Gaël
Out[16]: 'Ga\xc3\xabl'

In [17]: filter_name('Stéfan')
---------------------------------------------------------------------------
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128)

In [17]: def achilles_arrow(x):
   ....:    if abs(x - 1) < 1e-3:
   ....:        raise StopIteration
   ....:    x = 1 - (1-x)/2.
   ....:    return x
   ....:

In [18]: x = 0

In [19]: while True:
   ....:     try:
   ....:         x = achilles_arrow(x)
   ....:     except StopIteration:
   ....:         break
   ....:
   ....:

In [20]: x
Out[20]: 0.9990234375