python scripts the fifth day

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

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")

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.")

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.")

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.")

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.") 

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.")