Welcome to my lessons

Bo Zhang (NAOC, mailto:bozhang@nao.cas.cn) will have a few lessons on python.

These are very useful knowledge, skills and code styles when you use python to process astronomical data.
All materials can be found on my github page.
jupyter notebook (formerly named ipython notebook) is recommeded to use

These lectures are organized as below:

install python
basic syntax
numerical computing
scientific computing
plotting
astronomical data processing
high performance computing
version control

object



In [1]:

    
object









    Out[1]:





object



In [2]:

    
dir()









    Out[2]:





['In',
 'Out',
 '_',
 '_1',
 '__',
 '___',
 '__builtin__',
 '__builtins__',
 '__doc__',
 '__name__',
 '_dh',
 '_i',
 '_i1',
 '_i2',
 '_ih',
 '_ii',
 '_iii',
 '_oh',
 '_sh',
 'exit',
 'get_ipython',
 'quit']



In [3]:

    
In









    Out[3]:





['', u'object', u'dir()', u'In']



In [4]:

    
a = 1.5
type(a)









    Out[4]:





float



In [5]:

    
print isinstance(a, float)
print isinstance(a, object)









    



True
True

Lists and Tuples



In [6]:

    
b = [1, 2, 3, 'abc']
type(b)









    Out[6]:





list



In [7]:

    
b.append(4)
b









    Out[7]:





[1, 2, 3, 'abc', 4]



In [8]:

    
c = (1, 2, 3, 'abc', 3)
type(c)









    Out[8]:





tuple



In [9]:

    
c.count(3)









    Out[9]:





2



In [10]:

    
c









    Out[10]:





(1, 2, 3, 'abc', 3)

Dictionaries and Sets



In [11]:

    
d = {'a': 123, 'b': 456}
d









    Out[11]:





{'a': 123, 'b': 456}



In [12]:

    
print d['a']
print d['b']



In [13]:

    
e = {1, 2}
print type(e)
e









    



<type 'set'>






    Out[13]:





{1, 2}

Iterators and Generators



In [14]:

    
%%time
for i in range(10):
    print i









    



0
1
2
3
4
5
6
7
8
9
CPU times: user 0 ns, sys: 0 ns, total: 0 ns
Wall time: 220 µs



In [15]:

    
%%time
for i in xrange(10):
    print i









    



0
1
2
3
4
5
6
7
8
9
CPU times: user 0 ns, sys: 0 ns, total: 0 ns
Wall time: 249 µs

mutable immutable
iterable



In [16]:

    
def f1yield(n):
    n0 = 0
    while n0 < n:
        yield n-n0
        n0 += 1

def f1print(n):
    n0 = 0
    while n0 < n:
        print n-n0
        n0 += 1

        
f = f1yield(5)
print type(f)
print f.next()
print f.next()
print f.next()
print f.next()


f = f1print(5)
print type(f)









    



<type 'generator'>
5
4
3
2
5
4
3
2
1
<type 'NoneType'>

Decorators



In [17]:

    
def salesgirl(method):
    def serve(*args):
        print "Salesgirl:Hello, what do you want?", method.__name__
        method(*args)
    return serve
   
@salesgirl
def try_this_shirt(size):
    if size < 35:
        print "I: %d inches is to small to me" %(size)
    else:
        print "I:%d inches is just enough" %(size)
try_this_shirt(38)









    



Salesgirl:Hello, what do you want? try_this_shirt
I:38 inches is just enough



In [18]:

    
print type(salesgirl)
print type(try_this_shirt)









    



<type 'function'>
<type 'function'>

lambda



In [19]:

    
def f2(x):
    return 2*x

l2 = lambda x: 2*x

print f2(10)
print l2(10)



In [20]:

    
print type(f2)
print type(l2)









    



<type 'function'>
<type 'function'>



In [21]:

    
print f2









    



<function f2 at 0x7f0b94286230>



In [22]:

    
print l2









    



<function <lambda> at 0x7f0b94286398>



In [ ]:

class

you should understand the difference between "class" and "instance"



In [23]:

    
class People():
    """here we define the People class
    """
    name = ''
    height = 180. # cm 
    weight = 140. # pound
    energy = 100. # percent
    energy_cost_per_work_hour = 10.    # percent energy per work hour
    energy_per_meal = 90. # percent energy per meal
    
    def __init__(self, name='', height=180., weight=140., energy=100.):
        self.name = name
        self.height = height
        self.weight = weight
        self.energy = energy
    
    def work(self, hours=1.):
        if hours > 0. and hours < 10. and hours < self.energy/self.energy_cost_per_work_hour:
            self.energy -= hours*self.energy_cost_per_work_hour
        else:
            if hours <= 0.:
                raise ValueError('@Cham: hours must be positive!')
            else:
                raise ValueError('@Cham: energy ran out!')
    
    def eat(self, num_meal=1.):
        if num_meal > 0. and num_meal <= 5.:
            self.energy += num_meal*self.energy_per_meal
            if self.energy > 100.:
                self.energy = 100.
        else:
            if num_meal <= 0.:
                raise ValueError('@Cham: number of meals must be positive!')
            else:
                raise ValueError('@Cham: too many meals!')
                
    def print_status(self):
        print ''
        print 'name:                      %s' % self.name
        print 'height:                    %s' % self.height
        print 'weight:                    %s' % self.weight
        print 'energy:                    %s' % self.energy
        print 'energy_cost_per_work_hour: %s' % self.energy_cost_per_work_hour
        print 'energy_per_meal:           %s' % self.energy_per_meal
        
jim = People('Jim')
jim.print_status()
jim.work(5)
jim.print_status()
jim.eat(2)
jim.print_status()









    



name:                      Jim
height:                    180.0
weight:                    140.0
energy:                    100.0
energy_cost_per_work_hour: 10.0
energy_per_meal:           90.0

name:                      Jim
height:                    180.0
weight:                    140.0
energy:                    50.0
energy_cost_per_work_hour: 10.0
energy_per_meal:           90.0

name:                      Jim
height:                    180.0
weight:                    140.0
energy:                    100.0
energy_cost_per_work_hour: 10.0
energy_per_meal:           90.0

HOMEWORK

use generator to generate the Fibonacci sequence
try to define a simple class



In [ ]: