Quick Overview

This assumes you know some coding
There are great tutorials that are more self paced
I just want you to continue to get a flavor of python

Indentation



In [2]:

    
#Indentation

a = [5,2,8,7]

for item in a:
    print item



In [3]:

    
for item in a:
    if item > 3:
        print item, 'is big'
    else:
        print item, 'is small'









    



5 is big
2 is small
8 is big
7 is big



In [4]:

    
# Comments

for item in a:
    if item > 3:
        # I think 3 is big
        print item, 'is big'
    else:
        print item, 'is small'









    



  File "<ipython-input-4-d9acce4396e0>", line 6
    else:
       ^
IndentationError: expected an indented block

Imports



In [5]:

    
# imports

import os
os?



In [8]:

    
whereami = os.getcwd()
print whereami









    



/user_home/w_cindeem



In [10]:

    
os.listdir(whereami)









    Out[10]:





['.anaconda',
 '03-Conditionals_and_Control_Flow.ipynb',
 'wakaripython',
 '.kshrc',
 'scripts',
 '2013_08_Pandas_Talk.ipynb',
 '.notebook.out.log',
 '.bashrc',
 '.ipython',
 '.gateone',
 '08-Loops.ipynb',
 '.bash_profile',
 '02-Strings.ipynb',
 'PandasPythonEssentials.ipynb',
 '.bash_logout',
 '.matplotlib',
 '01-Intro.ipynb',
 '.emacs',
 '.continuum']

Variables and Pass-by-reference gotchas



In [18]:

    
# Variables and gotchas

a = [1,2,3]
b = a
print 'a=', a, 'b=', b









    



a= [1, 2, 3] b= [1, 2, 3]



In [19]:

    
a.append(42)
print 'b is', b









    



b is [1, 2, 3, 42]

Dynamic typing and Strong References



In [23]:

    
myint = 3
mystr = '3'
print 'myint is of ', type(myint)
print 'mystr is of ', type(mystr)









    



myint is of  <type 'int'>
mystr is of  <type 'str'>



In [24]:

    
myint + mystr









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-24-4df3310450c6> in <module>()
----> 1 myint + mystr

TypeError: unsupported operand type(s) for +: 'int' and 'str'



In [25]:

    
myint * mystr









    Out[25]:





'333'



In [26]:

    
print myint / 22
print myint / 22.0









    



0
0.136363636364



In [27]:

    
mystr.









    



  File "<ipython-input-27-3412e27a46e3>", line 1
    mystr.?
          ^
SyntaxError: invalid syntax

Binary Operators and Comparisons



In [28]:

    
myint > 0









    Out[28]:





True



In [29]:

    
#remember above where we defined b = a?
a is b









    Out[29]:





True



In [31]:

    
print a
a is [1,2,3,42]









    



[1, 2, 3, 42]






    Out[31]:





False



In [32]:

    
a == [1,2,3,42]
#beware accidentally doing this
# a = [1,2,3,42]









    Out[32]:





True

mutable and immutable



In [35]:

    
mylist = ['a','b','c']
print 'original', mylist
mylist[0] = 'hey im different'
print 'new', mylist









    



original ['a', 'b', 'c']
new ['hey im different', 'b', 'c']



In [37]:

    
# small indexing aside, python indexes from 0
print mylist[0]
print mylist[1:2] #left inclusive, right NOT inclusive









    



hey im different
['b']



In [38]:

    
print mylist[-1]



In [39]:

    
mytuple = ('a','b','c')
mytuple[0] = '32'









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-39-af539ccac9b0> in <module>()
      1 mytuple = ('a','b','c')
----> 2 mytuple[0] = '32'

TypeError: 'tuple' object does not support item assignment

Data Types

int
float
boolean
None



In [40]:

    
myint = 1
myfloat = 1.0
mybool = True
nothing = None



In [42]:

    
# datetime
from datetime import datetime, date, time

mydatetime = datetime(2013, 9, 6, 11,22)
print mydatetime.day



In [50]:

    
print mydatetime.strftime('%Y-%m-%d')
print mydatetime.strftime('%b %d, %Y')









    



2013-09-06
Sep 06, 2013



In [51]:

    
import dateutil



In [52]:

    
dateutil.parser.parse('May 23 2013')









    Out[52]:





datetime.datetime(2013, 5, 23, 0, 0)

Control Flow

for
if, elif, else
while
pass

A container holds things (like strings, ints, floats, etc)

for thing in container:

# (I now have  thing)

do something with this thing



In [53]:

    
for item in [1,'b',3,'a', 42]:
    if item > 0:
        print item



In [60]:

    
for something in [1,'b',3,'a', 42]:
    if isinstance(something, str):
        print  'str', something
    elif something > 1:
        pass
    else:
        print something









    



1
str b
str a



In [63]:

    
count = 0
while count < 5:
    orig = count
    print orig
    count += 1
    print 'updated', count









    



0
updated 1
1
updated 2
2
updated 3
3
updated 4
4
updated 5

Exceptions



In [70]:

    
bucket = [1,2,3,'alligator']
for thing in bucket:
    try:
        print thing, 22 + thing
    except:
        raise ValueError('Cant add 22 to %s'%thing)









    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-70-276386ea0bb8> in <module>()
      4         print thing, 22 + thing
      5     except:
----> 6         raise ValueError('Cant add 22 to %s'%thing)

ValueError: Cant add 22 to alligator





    



 1 23
2 24
3 25
alligator

Getting a Range of numbers

range : generated a list of values

xrange : iterator that generates list of values one-by-one

enumerate : counts your items for you



In [72]:

    
for anint in range(5):
    print anint



In [73]:

    
for val, thingy in enumerate(['spam', 'eggs', 'foo', 'bar']):
    print thingy, 'is', val









    



spam is 0
eggs is 1
foo is 2
bar is 3



In [ ]: