hi all

type -a python{,w,2.3,2.4,2.5}
fink list python24 ipython

[ -f /sw/bin/init.sh ] && source /sw/bin/init.sh
less ~/.bashrc
source ~/.bashrc

fink install ipython-py24

Notes:
-------

type() gives you the type of an entitiy.
'''  /// 
'''
Spans multiple lines.

Set a variable:
In [10]: aStr="some old string"

In [11]: aStr
Out[11]: 'some old string'

# Index a variable. A string is an array. Index with brackets.
In [12]: aStr[0]
Out[12]: 's'

# A slice of an array.
In [13]: aStr[5:8]
Out[13]: 'old'

# Index from the back.
In [14]: aStr[5:-1]
Out[14]: 'old strin'

# To get a list of methods for an object type
object.<tab>

# Remember to add () to the methods, since they're functions.
aStr.islower()
Out[20]: True

# Replace characters
In [22]: aStr.replace('i','*')
Out[22]: 'some old str*ng'

# Note print evaluates things like \t
In [23]: aStr         
Out[23]: 'some old string'

In [24]: aStr.replace('o','\t')
Out[24]: 's\tme \tld string'

In [25]: print aStr.replace('o','\t')
s       me      ld string

In [26]: print "hello world"
hello world

In [27]: print "hello","world"
hello world

# Note how to concatinate strings. You can't embed aStr within the quotes 
# and have it interpreted.
In [29]: print "before "+aStr+ " after"
before some old string after

# Find finds the first occurance of a character
In [31]: aStr.find('d')
Out[31]: 7

# But it it doesn't find it, you get a -1.
In [32]: aStr.find('x')
Out[32]: -1

# To find out about a function, append a '?'
In [33]: aStr.find?    
Type:           builtin_function_or_method
Base Class:     <type 'builtin_function_or_method'>
String Form:    <built-in method find of str object at 0x113c2a0>
Namespace:      Interactive
Docstring:
    S.find(sub [,start [,end]]) -> int
    
    Return the lowest index in S where substring sub is found,
    such that sub is contained within s[start,end].  Optional
    arguments start and end are interpreted as in slice notation.
    
    Return -1 on failure.

# To split a line on white space (default delimter):
In [34]: aStr.split()
Out[34]: ['some', 'old', 'string']

# Make a string with comma delimiters:
In [35]: anotherStr='10,20,30,405,something' 

In [37]: anotherStr.split(',')
Out[37]: ['10', '20', '30', '405', 'something']

# Assign the resulting list in a variable.
In [38]: aList=anotherStr.split(',')

In [39]: aList[2]
Out[39]: '30'

# Lists are Arrays.
In [41]: newList=[]

# You can even have lists of lists in python. 
In [39]: listoflist = [ [1,2,3], 'two']

In [40]: print listoflist
[[1, 2, 3], 'two']

# Append with a list as the argument, inserts the list as a single new item.
In [43]: newlist=['a','b']
In [45]: newlist.append(aList)

In [46]: newlist
Out[46]: ['a', 'b', ['10', '20', '30', '405', 'something']]

# But to append a list onto a list use a "+"
In [47]: newlist+aList        
Out[47]: 
['a',
 'b',
 ['10', '20', '30', '405', 'something'],
 '10',
 '20',
 '30',
 '405',
 'something']

# See how range works:
In [48]: range(2,4)
Out[48]: [2, 3]

In [49]: range(2,5)
Out[49]: [2, 3, 4]

In [50]: range(0,10,2)
Out[50]: [0, 2, 4, 6, 8]

# Check out this cool way to make an array:
List comprehension
In [51]: [ x*.1 for x in range(2,15,3) ]   
Out[51]: 
[0.20000000000000001,
 0.5,
 0.80000000000000004,
 1.1000000000000001,
 1.4000000000000001]

# Math functions:
In [51]: import math

In [52]: math.
math.__class__         math.__str__           math.frexp
math.__delattr__       math.acos              math.hypot
math.__dict__          math.asin              math.ldexp
math.__doc__           math.atan              math.log
math.__file__          math.atan2             math.log10
math.__getattribute__  math.ceil              math.modf
math.__hash__          math.cos               math.pi
math.__init__          math.cosh              math.pow
math.__name__          math.degrees           math.radians
math.__new__           math.e                 math.sin
math.__reduce__        math.exp               math.sinh
math.__reduce_ex__     math.fabs              math.sqrt
math.__repr__          math.floor             math.tan
math.__setattr__       math.fmod              math.tanh

# To put everything in the upper level name space you can execute
from math import *

# So now you don't have to type math.<function> (e.g. math.pi). You can just 
# type "pi". But this will clobber functions in the upper name space that 
# have the same name.

# You could however just pull in one function at a time
from math import pi

# No complex numbers for sqrt
In [58]: math.sqrt(-1)
Out[58]: nan

# But complex numbers are generally built in.
In [59]: 2+3j
Out[59]: (2+3j)

# To get just the imaginary part:
In [62]: a=(2+3j)*(3-3j)

In [63]: a.imag
Out[63]: 3.0

# To handle floating point numbers and not get odd bit rounding, use the 
# decimal module. It has an object called Decimal that you can use for floats
# that will look more reasonable.
import decimal

decimal.Decimal(".1")+3
Out[75]: Decimal("3.1")

# Note the Decimal object here is a number that you can add other things to.

# Type conversions:
# to convert to ints:
int(string)
# To convert to strings:
str(num)
# To convert to a float:
float(string)

# If you're parsing data in a file, those will come in very handy, because
# everything will be read in as strings. You'll have to convert numbers to 
# the appropriate type.

# Conditionals (ifs)
In [79]: if 1<2: print 'yes'
   ....: else: print 'no'
   ....: 
yes

# or
In [80]: if 1<2:
   ....:     print 'yes'
   ....: else:
   ....:     print 'no'
   ....:     
   ....:     
yes

# Indenting is CRITICAL:
In [81]: if 1<2:
   ....:     print 'yes'
   ....:        print 'error'
------------------------------------------------------------
IndentationError: unindent does not match any outer indentation level (<ipython console>, line 3)

# Booleans are capitalized
In [82]: print (1<2)
True

In [83]: print (1>2)
False

In [84]: print (1==2)
False

# For Loops:
# using our range command
In [85]: for i in range(2,9):
   ....:     print i
   ....:     
2
3
4
5
6
7
8

# Continue in a loop:
NameError: name 'x' is not defined

In [88]: for i in range(1,10):
   ....:     if i==5: continue
   ....:     print i
   ....:     
   ....:     
1
2
3
4
6
7
8
9

# Looping over a list:
In [92]: for z in ['one', 2,'three']:
   ....:     print type(z),'---->', z
   ....:     
   ....:     
<type 'str'> ----> one
<type 'int'> ----> 2
<type 'str'> ----> three

# ipython can do shell stuff:
In [93]: pwd
Out[93]: '/Users/vschmidt'

In [94]: cd /Users/vschmidt/svnsandbox/python_misc/trunk/
/Users/vschmidt/svnsandbox/python_misc/trunk

In [95]: ls
myfile.txt      test.py

In [96]: pwd
Out[96]: '/Users/vschmidt/svnsandbox/python_misc/trunk'

# Reading from a file:
# "open" and "file" are the same thing. But you never use "open"
In [97]: for line in file('myfile.txt'):
   ....:     print line
   ....:     
   ....:     
First line

2nd line

etc


# But notice that you get an extra \n for each line.
# To "chomp" (that's a perl thing) the \n off the end, add a comma
In [98]: for line in file('myfile.txt'):
   ....:     print line,
   ....:     
   ....:     
First line
2nd line
etc

# Print puts a \n at the end of everything you print by default. To 
# NOT print the \n, append a comma to your print statement.
In [99]: print 1,; print 2,; print 3,
1 2 3

In [100]: print 1,; print 2,; print 3 
1 2 3

In [101]: print 1,; print 2; print 3
1 2
3

# Here we make a file in the bash shell:
valsmac:~/svnsandbox/python_misc/trunk vschmidt$ cat << EOF > my.dat
> 1 2 
> 3 4
> 1.2 3.4
> EOF

# Here we open a text file, read in the values and add them rowwise:
In [104]: for line in file('my.dat'):
   .....:     fields=line.split()
   .....:     total = float(fields[0]) + float(fields[1])
   .....:     print total
   .....:     
   .....:     
3.0
7.0
4.6

# To get the time:
import datetime

In [119]: datetime.datetime.utcnow()
Out[119]: datetime.datetime(2006, 10, 31, 15, 52, 26, 383943)

# To get the month:
datetime.datetime.utcnow().month

# To add or subtract time:
In [123]: datetime.datetime.utcnow() + datetime.timedelta(days=1)
Out[123]: datetime.datetime(2006, 11, 1, 15, 55, 12, 631363)

In [124]: datetime.datetime.utcnow() + datetime.timedelta(days=-1)
Out[124]: datetime.datetime(2006, 10, 30, 15, 55, 19, 264891)

# The time module:
import time

# To sleep
time.sleep(3)

# Help for modules:
help(datetime)
Then bring up the URL in a browser for better documentation of the module.

# Writing to a file:
# Opening a file for writing (over-writing actually)
In [157]: out = file('out.dat','w')

# Writing to the file:

In [158]: for i in range(10):
   .....:     time.sleep(1.1)
   .....:     t=datetime.datetime.utcnow()
   .....:     timeStamp=str(time.mktime(t.timetuple()))
   .....:     out.write(str(i)+' '+str(math.sin(i/4.0))+' '+str(timeStamp)+'\n')
   .....:     
   .....:     

In [160]: out.close()
# NOTE the data is not actually written until you close the file.


# LOOK OUT FOR INTEGER DIVISION
In [151]: 1/4
Out[151]: 0

In [152]: 1/4.0
Out[152]: 0.25

In [153]: 1/4.
Out[153]: 0.25



From Kurt

filename = 'out.dat'
iterations=10
stepSize=1.1
out = file(filename,'w')

for i in range(iterations):
	time.sleep(stepSize)
	t = datetime.datetime.utcnow()
	timeStamp = str(time.mktime(t.timetuple()))
	out.write(str(i)+' '+str(math.sin(i*stepSize))+' '+timeStamp+'\n')

# gnuplot aside:
# To plot 3-column data in 3D plot (in this case with time on third axis).
# within gnuplot

splot "out.dat" with lp

# How to write a python script:

#!/usr/bin/env python

# This uses the first python of all of them listed on this machine, 
# specified in your path. This is the safe way to build a script. 
# Remember don't use "which" to figure out what's in your path, use this
# instead:

vschmidt$ type -a python
python is /sw/bin/python
python is /usr/bin/python

# So the one in /sw/bin/python will be executed.