Python in 90mins

Larry cai <larry.caiyu@gmail.com>

 What is python ? Why Python ?
 Exercise 1: Hello World
 Exercise 2: String, List via command line
 Exercise 3: For loop with if..else..
 Exercise 4: Learn how to use module json to dump data
 Exercise 5: Generate online NASDAQ data using json
!!! Lots of materials are copied from
http://www.cs.columbia.edu/~hgs/teaching/ap/slides/python.ppt and which is
based on official tutorial by Guido van Rossum
Exercises are created by Larry Cai
Python in 90 minutes2

What is Python ? And Why Python 2.7
 Python is an easy to learn, powerful script programming
language
 Python is mature and better community compare to Perl
 Python is high level over shell script
 Python is well supported in OS as default compare to
Ruby (which is also nice)
 Python 3.x is quite new, not well accepted
 Welcome to Python world

 Python 2.7.x In Windows with Git Bash
 http://www.python.org/ftp/python/2.7.3/python-2.7.3.msi
 Add into Path
 How to run ?
 /usr/local/bin/python
 #!/usr/bin/env python
 interactive use
Python 2.7.3 (default,Apr 10 2012, 23:24:47) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
 $ python script.py

 Hello World
 hello.py
#!/usr/bin/env python
for name in [“larry”,”cai”]:
print "hello" , name

Tips: Indent is important for python
 Visible symbol in your favorite editor
Python forces to use a certainPython forces to use a certain
indentation style instead of “{,}”indentation style instead of “{,}”

Basic operations & program
 Assignment:
 size = 40
 a = b = c = 3
 Numbers
 integer, float
 complex numbers: 1j+3,
abs(z)
 Strings
 'hello world',
'it's hot'
 "bye world"
 continuation via or use """
long text """"
a,b = 0, 1
# non-zero = true
while b < 10:
# formatted output,
without n
print b,
# multiple assignment
a,b = b, a+b

String & List operations
 concatenate with + or
neighbors
 word = 'Help' + x
 word = 'Help' 'a'
 subscripting of strings
 'Hello'[2]  'l'
 slice: 'Hello'[1:2]  'el'
 word[-1]  last character
 len(word)  5
 immutable: cannot assign to
subscript
 lists can be heterogeneous
 a = ['spam', 'eggs',
100, 1234, 2*2]
 Lists can be indexed and
sliced:
 a[0]  spam
 a[:2]  ['spam', 'eggs']
 Lists can be manipulated
 a[2] = a[2] + 23
 a[0:2] = [1,12]
 a[0:0] = []
 len(a)  5

Learn the standard script sample
https://gist.github.com/4308811
Help doc
Import library
Function
Main func
Start here !

Exercise 2: remove characters
 Practices basic operation in Interactive Shell
 Add features to remove two characters each from input
 ./hello2.py -m larry,cai
hello rry
hello i
Hints: nameHints: names = messages.split(“,”)s = messages.split(“,”)

Control flow: if & for
x =
int(raw_input("Please
enter #:"))
if x < 0:
x = 0
print 'Negative
changed to zero'
elif x == 0:
print 'Zero'
elif x == 1:
print 'Single'
else:
print 'More'
 no case statement
a = ['cat', 'window',
'defenestrate']
for x in a:
print x, len(x)
 no arithmetic
progression, but
 range(10)  [0, 1, 2,
3, 4, 5, 6, 7, 8, 9]
 for i in
range(len(a)):
print i, a[i]
 do not modify the
sequence being iterated
over

Loops: break, continue, else, o nothing
 break and continue
like C
 else after loop
exhaustion
for n in range(2,10):
for x in range(2,n):
if n % x == 0:
print n, 'equals',
x, '*', n/x
break
else:
# loop fell through
without finding a factor
print n, 'is prime'
 pass does nothing
 syntactic filler
while 1:
pass

Exercise 3: for loop with if..else..
 ./hello2.py -m larry,cai,in,github
1. hello Larry
2. hello Cai
3. @
4. hello Github
Hints: think about loop in clean wayHints: think about loop in clean way

Defining functions
def fib(n):
"""Print a Fibonacci
series up to n."""
a, b = 0, 1
while b < n:
print b,
a, b = b, a+b
>>> fib(2000)
 First line is docstring
 first look for variables in
local, then global
 need global to assign global
variables
def ask_ok(prompt,
retries=4, complaint='Yes
or no, please!'):
while 1:
ok = raw_input(prompt)
if ok in ('y', 'ye',
'yes'): return 1
if ok in ('n', 'no'):
return 0
retries = retries - 1
if retries < 0: raise
IOError, 'refusenik
error'
print complaint
>>> ask_ok('Really?')

Modules
 import module:
import fibo
 Use modules via "name
space":
>>> fibo.fib(1000)
>>> fibo.__name__
'fibo'
 can give it a local name:
>>> fib = fibo.fib
>>> fib(500)
 function definition +
executable statements
 executed only when module
is imported
 modules have private symbol
tables
 avoids name clash for global
variables
 accessible as
module.globalname
 can import into name space:
>>> from fibo import fib,
fib2
>>> fib(500)
 can import all names defined
by module:
>>> from fibo import *

Exercise 4: write into json config file
 JSON (JavaScript Object Notation) dump list of the
messages into external config files
 ./hello2.py -m larry,cai,in,github > config.json
 $ cat config.json
[
“larry”,
“cai”,
“in”,
“github”
]
Hints: json.dumps(data, indent=2)Hints: json.dumps(data, indent=2)

Tuples and sequences
 lists, strings, tuples: examples
of sequence type
 tuple = values separated by
commas
>>> t = 123, 543, 'bar'
>>> t[0]
123
>>> t
(123, 543, 'bar')
 Tuples may be nested
>>> u = t, (1,2)
>>> u
((123, 542, 'bar'), (1,2))
 Empty tuples: ()
>>> empty = ()
>>> len(empty)
0
 sequence unpacking  distribute
elements across variables
>>> t = 123, 543, 'bar'
>>> x, y, z = t
>>> x
123
 packing always creates tuple
 unpacking works for any sequence

Dictionaries
 like Tcl or awk associative
arrays
 indexed by keys
 keys are any immutable type:
e.g., tuples
 but not lists (mutable!)
 uses 'key: value' notation
>>> tel = {'hgs' : 7042, 'lennox':
7018}
>>> tel['cs'] = 7000
>>> tel
 no particular order
 delete elements with del
>>> del tel['foo']
 keys() method  unsorted list of
keys
>>> tel.keys()
['cs', 'lennox', 'hgs']
 use has_key() to check for existence
>>> tel.has_key('foo')
0

Exercise 5: Generate report from internet
 Print MSFT, GOOG stock via Nasdaq live JSON with sort
 ./hello2.py –s MSFT,GOOG
“Getting live data from NASDAQ @ <current time>
GOOG: xx
MSFT: xx
$ curl -x <proxy> "http://finance.google.com/finance/info?client=ig&q=NASDAQ:MSFT,NASDAQ:GOOG “
fl = urlopen (“link”)
data = json.loads(contents)
[
{
"id": "694653"
,"t" : "GOOG"
,"e" : "NASDAQ"
,"l" : "701.96"
,"l_cur" : "701.96"
,"s": "0"
,"ltt":"4:00PM EST"
,"lt" : "Dec 14, 4:00PM EST"
,"c" : "-0.74"
,"cp" : "-0.10"
,"ccol" : "chr"
}
]
Hints: urlopen -> json.load -> data ..Hints: urlopen -> json.load -> data ..

 Automate your daily work in python scripts
 Keep coding in python !!!
 Reading books and sample codes !!

 Slides:
 http://www.slideshare.net/doughellmann/an-introduction-to-
the-zen-of-python - Doug Hellmann
 http://www.cs.columbia.edu/~hgs/teaching/ap/slides/python.ppt
 List books, articles, and electronic sources
 http://docs.python.org/2.7/
 Python cheatsheet: http://www.addedbytes.com/cheat-
sheets/python-cheat-sheet/
 Example for last exercise
 http://digitalpbk.com/stock/google-finance-get-stock-quote-realtime

Python in 90mins

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