My python2 pocket reference - 20151212

This is a first version of python2 pocket reference.

Conditions

There is no syntax like switch, case, cond. Only if-elif-else is available.

>>> X = 100
>>> if X == 10:
...   print 'X is 10'
... elif X == 20:
...   print 'X is 20'
... else:
...   print 'X is something else'
... 
X is something else
>>> 

Samples handling string and character

convert character to ascii code, like char-code

>>> ord('A')
65
>>>

convert ascii code to character, like code-char

>>> chr(65)
'A'
>>>

convert string to byte array

>>> import array
>>> array.array('B', "aaa")
array('B', [97, 97, 97])
>>> x = array.array('B', "aaa")
>>> x
array('B', [97, 97, 97])
>>> x[1]
97
>>> x[2]
97
>>> x[3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: array index out of range
>>>

convert byte array to string with default encoding

>>> x = [97,98,99]
>>> ''.join(map(chr,x))
'abc'
>>>

substring

>>> X = "0123456789"
>>> Y = X[0:5]
>>> Y
'01234'
>>>

find any characters in string

>>> X = "2000/12/31"
>>> X.find('/')
4
>>> X.rfind('/')
7
>>> X = "This is a pen."
>>> X.find('is')
2
>>> X.rfind('is')
5
>>> X.find('pen')
10
>>> 

Basic File IO

Read from existed files, using 'r'

>>> with open('test.txt','r') as f:
...   for line in f:
...     print line
... 
Test

>>>
***Write to some files, using 'w'
>|python|
>>> with open('test.txt', 'r') as f:
...   for line in f:
...     print line
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'test.txt'
>>> with open('test.txt', 'w') as f:
...   f.write('This is a test message.')
... 
>>> with open('test.txt', 'r') as f:
...   for line in f:
...     print line
... 
This is a test message.
>>> 

Socket Handling

TCP client as using context, reference is https://stackoverflow.com/questions/16772465/how-to-use-socket-in-python-as-a-context-manager

import argparse
import socket
from contextlib import contextmanager

@contextmanager
def tcp_connect_to(*args, **kwargs):
    s = socket.create_connection(*args, **kwargs)
    try:
        yield s
    finally:
        s.close()

parser = argparse.ArgumentParser(description = 'Command Line Argument Parser')
parser.add_argument('-host', dest = 'host', required = True)
parser.add_argument('-port', dest = 'port', required = True)
argument = parser.parse_args()
x = vars(argument)

dest = (x['host'], int(x['port']))

with tcp_connect_to(dest) as s:
    s.send("Hello!")
    ...

UDP client as using context, reference is same as TCP

import argparse
import socket
from contextlib import contextmanager

@contextmanager
def udp_connect_to():
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    try:
        yield s
    finally:
        s.close()

parser = argparse.ArgumentParser(description = 'Command Line Argument Parser')
parser.add_argument('-host', dest = 'host', required = True)
parser.add_argument('-port', dest = 'port', required = True)
argument = parser.parse_args()
x = vars(argument)

dest = (x['host'], int(x['port']))

with udp_connect_to() as s:
    s.sendto("Hello", dest)
    data, server = s.recvfrom(8192)
    print '%s returns %s' % server, data