python scripts the fifth day

第五天了。
先祝咱们周末愉快！
说起来python，学习有段时间了。一定要坚持下去。
做事不能一蹴而就，先来个温故而知新吧。

1，readit.py

print "Opening and closing the file."
text_file=open("read_it.txt", "r")
# before you can read from a text file, you need to open it
# i don't include any path information
# python looks in the current directory for the file
text_file.close()
# whenever you've done with a file, close it

print "\nReading characters from the file."
text_file=open("read_it.txt", "r")
print text_file.read(1)
print text_file.read(5)
print text_file.read()
text_file.close()

print "\nReading one line at a time."
text_file=open("read_it.txt", "r")
print text_file.readline()
print text_file.readline()
print text_file.readline()
text_file.close()

print "\nReading the entire file into a list."
text_file=open("read_it.txt","r")
lines=text_file.readlines()
print lines
print len(lines)
for line in lines:
	print line
text_file.close()

print "\nLooping through the file, line by line."
text_file=open("read_it.txt", "r")
for line in text_file:
	print line
text_file.close()

raw_input("\nPress the enter key to exit.")

# "r"	read from a file. 
# "w"	write to a file
# "a"	append a file
# "r+"	read from and write to a file
# "w+"	write to and read from a file
# "a+" 	append and read from a file

2，writeit.py

print "creating a text file with the write() method."
text_file=open("write_it.txt", "w")

text_file.write("line 1\n")
text_file.write("this is line 2\n")
text_file.write("that makes this line 3\n")
# write() method doesn't automatically insert a newline character 
# at the end of a string it writes
# you have to put newlines in where you want them
text_file.close()

print "\nReading the newly created file."
text_file=open("write_it.txt", "r")
print text_file.read()
text_file.close()

print "\nCreating a text file with the writelines() method."
text_file=open("write_it2.txt", "w")
lines = ["line 1\n",
		"this is line 2\n",
		"that makes this line 3\n"]
text_file.writelines(lines)
text_file.close()

print "\nReading the newly created file"
text_file=open("write_it2.txt", "r")
print text_file.read()
text_file.close()

raw_input("\nPress the enter key to exit")

3,pickleit.py

import cPickle, shelve
print "Pickling lists."
variety=["sweet", "hot", "dill"]
shape=["whole", "spear", "chip"]
brand=["claussen", "heinz", "vlassic"]
pickle_file=open("pickles1.dat", "w")
cPickle.dump(variety, pickle_file)
cPickle.dump(shape, pickle_file)
cPickle.dump(brand, pickle_file)
pickle_file.close()

print "\nUnpickling lists."
pickle_file=open("pickles1.dat", "r")
variety=cPickle.load(pickle_file)
shape=cPickle.load(pickle_file)
brand=cPickle.load(pickle_file)

print variety, "\n", shape, "\n" , brand
pickle_file.close()

print "\nShelving lists."
pickles=shelve.open("pickles2.dat")
# shelve.open() function works with a file that stores pickled objects and not characters.

pickles["variety"]=["sweet", "hot", "dill"]
pickles["shape"]=["whole", "spear", "chip"]
pickles["brand"]=["claussen", "heinz", "vlassic"]
pickles.sync()        # make sure data is written

print "\nRetrieving the lists from a shelved file:"
for key in pickles.keys():
	print key, "-", pickles[key]

raw_input("\nPress the enter key to exit.")

4,handleit.py

try:
	num=float(raw_input("Enter a number:"))
except:
	print "something went wrong!"

# IOError
# IndexError
# KeyError
# NameError
# SyntaxError
# TypeError
# ValueError
# ZeroDivisionError

# specifying exception type
try:
	num=float(raw_input("\nEnter a number:"))
except (ValueError):
	print "That was not a number!"

# if you're not sure what the exception type is
# just create the exception 

# handle multiple exceptions
print
for value in (None, "Hi!"):
	try:
		print "Attempting to convert", value, "-->",
		print float(value)
	except (TypeError, ValueError):
		print "Something went wrong!"
	except (TypeError):
		print "I can only convert a string or a number!"
	except (ValueError):
		print "i can only convert a string of digits!"
	
# get an exception's argument
try:
	num=float(raw_input("\nEnter a number:"))
except (ValueError) , e:
	print "That was not a number. or as python would say: \n", e

# try/except/else
try:
	num=float(raw_input("\nEnter a number:"))
except (ValueError):
	print "That was not a number"
else:
	print "You entered the number", num

raw_input("\nPress the enter key to exit.")

5,simple_critter.py

class Critter(object):
	""" A virtual pet"""
	def talk(self):
		print "Hi, I'm an  instance of class Critter."
		# you can think of methods as functions associated with an object
		# every method must have a special first parameter, called self by convention
		# it provides a way for a method to refer to the object itself

# main
crit=Critter()
crit.talk()

raw_input("\nPress the enter key to exit.")

6,constructor.py

class Critter(object):
	""" A virtual pet. """
	def __init__(self):
		print "A new critter has been born!"
	# constructor method (initialization method)
	# python has a collection of built-in "special methods" 
	# whose names begin and end with two underscores, the constructor method
		
	def talk(self):
		print "\nHi i'm an instance of class critter"
	
# main
crit1=Critter()
crit2=Critter()

crit1.talk()
crit2.talk()

raw_input("\nPress the enter key to exit.")

7,attribute.py

class Critter(object):
	" " " A virtual pet " " "
	def __init__(self, name):
		print " A new critter has been born."
		self.name=name
		
	def __str__(self):
		rep="critter object\n"
		rep+="name:"+ self.name + "\n"
		return rep
	def talk(self):
		print " Hi, I'm ", self.name, "\n"
	
# main
crit1=Critter("Poochie")
crit1.talk()

crit2=Critter("Randolph")
crit2.talk()

print "Printing crit1:"
print crit1

print "Directly accessing crit1.name:"
print crit1.name

raw_input("\nPress the enter key to exit.")

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