f = open("a.txt", "w")
f.write("hello")
f.close()

with open("a.txt", "w") as f:
    f.write("hello")

f = open("a.txt")
dir(f)

import os
class chdir:
    def __init__(self, dir):
        self.dir = dir
        print "__init__"
        
    def __enter__(self):
        print "__enter__"
        self.olddir = os.getcwd()
        os.chdir(self.dir)
        return self
        
    def __exit__(self, *a):
        print "__exit__"
        os.chdir(self.olddir)

print os.getcwd()
print "before with"
with chdir("/tmp") as x:
    print os.getcwd()
print "after with"
print os.getcwd()

import sys
from StringIO import StringIO

oldstdout = sys.stdout
buf = StringIO()
sys.stdout = buf
print "hello"
print "world"
sys.stdout = oldstdout
print "captured", repr(buf.getvalue())

# solution

from StringIO import StringIO
import sys

class capture_output:
    def __init__(self):
        self.buf = StringIO()

    def __enter__(self):
        self.oldstdout = sys.stdout
        sys.stdout = self.buf
        return self.buf
        
    def __exit__(self, type, exc, traceback):
        sys.stdout = self.oldstdout
    
#with capture_output() as buf:
#    print "hello"

capture_output()

print "hello"

#out = buf.getvalue()
#print "captured", repr(out)

class ignore_exception:
    def __init__(self):
        pass

    def __enter__(self):
        pass
        
    def __exit__(self, type, exc, traceback):
        print type, exc, traceback
        return True

with ignore_exception():
    print "begin"
    raise IOError("fo")