Python 初体验（五）

• python也有逻辑上的分行键\。类似MATLAB里面的…
• input and output

#!/usr/bin/python
# Filename: using_file.py
poem = '''\
Programming is fun
When the work is done
if you wanna make your work also fun:
use Python!
'''
f = file('poem.txt', 'w') # open for 'w'riting
f.write(poem) # write text to file
f.close() # close the file
f = file('poem.txt') # if no mode is specified, 'r'ead mode is assumed by default
while True:
    line = f.readline()
    if len(line) == 0: # Zero length indicates EOF
        break
    print line, # Notice comma to avoid automatic newline added by Python
f.close() # close the file

注意python打开文件时默认的打开方式是读打开

 

• 异常

#!/usr/bin/python
# Filename: raising.py
class ShortInputException(Exception):
    '''A user-defined exception class.'''
    def __init__(self, length, atleast):
        Exception.__init__(self)
        self.length = length
        self.atleast = atleast
        
try:
    s = raw_input('Enter something --> ')
    if len(s) < 3:
        raise ShortInputException(len(s), 3)
# Other work can continue as usual here
except EOFError:
    print '\nWhy did you do an EOF on me?'
except ShortInputException, x:
    print 'ShortInputException: The input was of length %d, \
was expecting at least %d' % (x.length, x.atleast)
else:
    print 'No exception was raised.'

注意到exception是可以raise滴，这对增加程序的鲁棒性很有好处

#!/usr/bin/python
# Filename: finally.py
import time
try:
    f = file('poem.txt')
    while True: # our usual file-reading idiom
        line = f.readline()
        if len(line) == 0:
            break
        time.sleep(2)
        print line,
finally:
    f.close()
    print 'Cleaning up...closed the file'

python延时的方法，python发生exception时会执行finally里面的语句块，这个程序中的作用是关掉文件