Python - 2. Jim Eng

Transcription

1 Python - 2 Jim Eng jimeng@umich.edu

2 Lists Dictionaries Try... except Methods and Functions Classes and Objects Midterm Review Overview

3 Patterns in programming - 1 Sequential steps Conditional steps Repeated steps Stored and reused steps

4 Patterns in programming - 2 Input Processing Output

5 pals = list() pals.append("glenn") pals.append("sally") pals.append("joe") print pals ['Glenn', 'Sally', 'Joe'] print pals[1] Sally

6 print pals ['Glenn', 'Sally', 'Joe'] pals[2] = 'Joseph' print pals ['Glenn', 'Sally', 'Joseph']

7 num = 1 for pal in pals:... print num, ") ", pal... num = num ) Glenn 2 ) Sally 3 ) Joseph print num 4

8 pals.sort() num = 1 for pal in pals:... print num, ") ", pal... num = num ) Glenn 2 ) Joseph 3 ) Sally

9 def print_list(list):... num = 1... for item in list:... print num, ") ", item... num = num print_list(pals) 1 ) Glenn 2 ) Joseph 3 ) Sally

10 pals.append('erin') pals.append('michele') pals.insert(3,'aaron') print_list(pals) 1 ) Glenn 2 ) Joseph 3 ) Sally 4 ) Aaron 5 ) Erin 6 ) Michele

11 nums = list() nums.append(12345) nums.append(15000) nums.append(13000) nums.append(12000) print_list(nums) 1 ) ) ) ) 12000

12 nums.append(12) print nums [12345, 15000, 13000, 12000, 12] nums.sort() print_list(nums) 1 ) 12 2 ) ) ) ) 15000

13 def foot_label(num):... label = "feet"... if(num == 1):... label = "foot"... return label... def inch_label(num):... label = "inches"... if(num == 1):... label = "inch"... return label...

14 def print_feet(inches_in):... feet = inches_in / inches = inches_in % msg = str(inches_in)... msg = msg + " inches equals " + str(feet)... msg = msg + " " + foot_label(feet)... if(inches > 0):... msg = msg + " and " + str(inches)... msg = msg + " " + inch_label(inches)... print msg...

15 print_feet(12000) inches equals 1000 feet print_feet(nums[1]) inches equals 1000 feet for num in nums:... print_feet(num) inches equals 1 foot inches equals 1000 feet inches equals 1028 feet and 9 inches inches equals 1083 feet and 4 inches inches equals 1250 feet

16 list2 = list() list2.append("jennifer") list2.append("jack") list2 ['Jennifer', 'Jack'] print list2 ['Jennifer', 'Jack'] print pals ['Glenn', 'Joseph', 'Sally', 'Aaron', 'Erin', 'Michele'] new_list = pals + list2 print new_list ['Glenn', 'Joseph', 'Sally', 'Aaron', 'Erin', 'Michele', 'Jennifer', 'Jack']

17 Lists are OK We can use them to keep things in order We can sort them -- pals.sort() We can add things to lists -- pals.append('joe'), pals.insert(3,'aaron') We can directly access individual items -- pals[2] We can iterate through the items -- for pal in pals: We can concatenate lists -- list3 = list1 + list2

18 pal = dict() pal['first'] = 'Gonzalo' pal['last'] = 'Silverio' pal[' '] = 'gsilver@example.org' pal['phone'] = ' ' print pal {'phone': ' ', 'last': 'Silverio', ' ': 'gsilver@example.org', 'first': 'Gonzalo'}

19 print pal['phone'] print pal['age'] Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: 'age'

20 print pal.get('age', 'Age not available') Age not available print pal.get('phone', 'Phone not available') print pal.get('age', 21) 21

21 for key in pal :... print key... phone last first

22 for key in pal :... print key, ": ", pal[key]... phone : last : Silverio gsilver@example.org first : Gonzalo

23 dir(pal) [' class ', ' cmp ', ' contains ', ' delattr ', ' delitem ', ' doc ', ' eq ', ' ge ', ' getattribute ', ' getitem ', ' gt ', ' hash ', ' init ', ' iter ', ' le ', ' len ', ' lt ', ' ne ', ' new ', ' reduce ', ' reduce_ex ', ' repr ', ' setattr ', ' setitem ', ' str ', 'clear', 'copy', 'fromkeys', 'get', 'has_key', 'items', 'iteritems', 'iterkeys', 'itervalues', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']

24 dir('hello') [..., 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill'] print 'Hello'.upper() HELLO print 'Hello'.swapcase() hello print 'lord of the rings'.title() Lord Of The Rings

25 dir(pal) [..., 'clear', 'copy', 'fromkeys', 'get', 'has_key', 'items', 'iteritems', 'iterkeys', 'itervalues', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']

26 pal.keys() ['phone', 'last', ' ', 'first'] pal.values() [' ', 'Silverio', 'Gonzalo'] pal.has_key('phone') True pal.has_key('age') False pal.items() [('phone', ' '), ('last', 'Silverio'), (' ', ('first', 'Gonzalo')]

27 pals = list() pal = dict() pal['first'] = 'Gonzalo' pal['last'] = 'Silverio' pal[' '] = 'gsilver@example.org' pal['phone'] = ' ' print pal {'phone': ' ', 'last': 'Silverio', ' ': 'gsilver@example.org', 'first': 'Gonzalo'} pals.append(pal)

28 pal = dict() print pal {} pal['first'] = 'Jim' pal['last'] = 'Eng' pal[' '] = 'jimeng@umich.edu' pal['phone'] = ' ' pals.append(pal) print pals [{'phone': ' ', 'last': 'Silverio', ' ': 'gsilver@example.org', 'first': 'Gonzalo'}, {'phone': ' ', 'last': 'Eng', ' ': 'jimeng@umich.edu', 'first': 'Jim'}]

29 for pal in pals:... for key in pal:... print key, ": ", pal[key]... print " ---- "... phone : last : Silverio gsilver@example.org first : Gonzalo ---- phone : last : Eng jimeng@umich.edu first : Jim ----

30 for pal in pals:... for key in keys:... print key, ": ", pal[key]... print " ---- "... first : Gonzalo last : Silverio phone : gsilver@example.org age : Traceback (most recent call last): File "<stdin>", line 3, in <module> KeyError: 'age'

31 for pal in pals:... for key in keys:... print key, ": ", pal[key]... print " ---- "... first : Gonzalo last : Silverio phone : gsilver@example.org age : Traceback (most recent call last): File "<stdin>", line 3, in <module> KeyError: 'age'

32 nk = " not known" for pal in pals:... for key in keys:... print key, ": ", pal.get(key, key + nk)... print " ---- "... first : Gonzalo last : Silverio phone : gsilver@example.org age : age not known birthday : birthday not known ---- first : Jim last : Eng phone : jimeng@umich.edu

33 person = dict() for key in keys:... val = raw_input(key + ": ")... person[key] = val... first: Denzel last: Washington phone: denzel@celeb.org age: 54 birthday: Dec 28 print person {'last': 'Washington', 'age': '54', 'phone': " ", 'birthday': 'Dec 28', ' ': 'denzel@celeb.org', 'first': 'Denzel'}

34 pals.append(person) pals [{'phone': ' ', 'last': 'Silverio', ' ': 'first': 'Gonzalo'}, {'phone': ' ', 'last': 'Eng', ' ': 'first': 'Jim'}, {'last': 'Washington', 'age': '54', 'phone': " ", 'birthday': 'Dec 28', ' ': 'first': 'Denzel'}]

35 Dictionaries are OK We can use a dictionary to associate keys and values We can describe an individual by its attributes We can iterate over the keys and access the values And so much more...

36 fahrenheit = input("enter F: ") celsius = convert(fahrenheit) print "C: ", celsius % python conv1.py Enter F: Fred Traceback (most recent call last): File "conv1.py", line 1, in <module> ftemp = input("enter F:"); File "<string>", line 1, in <module> NameError: name 'Fred' is not defined

37 print int('42') 42 print int(42.5) 42 print int('forty-two') Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: invalid literal for int() with base 10: 'forty-two'

38 try:... print int('42')... except:... print 'oops' try:... print int('forty-two')... except:... print 'oops'... oops

39 def safeint(val):... try:... print int(val)... except:... print 'oops'... safeint(42) 42 safeint(42.5) 42 safeint('42') 42 safeint('forty-two') oops

40 f = input("enter the temperature in farenheit: ") c = convert(f) print "The temperature in celsius is ", c $ python conv1.py Enter the temperature in farenheit: Fred Traceback (most recent call last): File "f2c.py", line 6, in <module> f = input("enter the temperature in farenheit: ") File "<string>", line 1, in <module> NameError: name 'Fred' is not defined

41 try: f = input("enter the temperature in farenheit: ") c = convert(f) print "The temperature in celsius is ",c except: print 'Please enter a temperature in farenheit'

42 $ python conv1.py Enter the temperature in farenheit: 212 The temperature in celsius is 100 $ $ python conv1.py Enter the temperature in farenheit: Fred Please enter a temperature in farenheit $ $ python conv1.py Enter the temperature in farenheit: 42.5 The temperature in celsius is $

43 Try... except We can "try" to execute parts of a program where errors might cause the program to crash We can "catch" errors and handle them gracefully

44 print len('abc') 3 print 'abc'.upper() ABC print 'abc'.isupper() False print type('abc') <type 'str'>

45 dir('abc') ['capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

46 print len('abc') 3 print 'abc'.upper() ABC print 'abc'.isupper() False print type('abc') <type 'str'>

47 pals = list() pals.append('a') pals.append('x') pals.append('b') pals.append('y') pals.append('c') pals.append('z') print pals ['a', 'x', 'b', 'y', 'c', 'z'] dir(pals) ['append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

48 print len(pals) 6 print type(pals) <type 'list'> print pals.count('b') 1 print pals.index('b') 2

49 class Simple(): num = 0 def incr(self): self.num = self.num + 1 return self.num def square(self): self.num = self.num * self.num return self.num def decr(self): self.num = self.num - 1 return self.num

50 x = Simple() print dir(x) print "x.num == ", x.num print "x.incr()",x.incr() print "x.incr()",x.incr) print "x.decr()",x.dec() print "x.incr()",x.incr() print "x.square()",x.square() print "x.decr()",x.decr() print type(x)

51 $ python simple.py [' doc ', ' module ', 'decr', 'incr', 'num', 'square'] x.num == 0 x.incr() 1 x.incr() 2 x.decr() 1 x.incr() 2 x.square() 4 x.decr() 3 <type 'instance'>

52 Classes and Objects We can define classes and then create instances of our classes A class encapsulates data and methods related to a particular type of object An instance of a class is an object We invoke methods on objects Sometimes we pass an object as a parameter to a function

53 Lists Dictionaries Try... except Methods and Functions Classes and Objects Midterm Review Overview