Introduction to Computing Using Python Dictionary container class + modules  Container Class dict  Modules, revisited

Introduction to Computing Using Python User-defined indexes and dictionaries >>> employee[ ] ['Yu', 'Tsun'] >>> employee[ ] ['Anna', 'Karenina'] >>> employee[ ] ['Hans', 'Castorp'] >>> employee[ ] ['Yu', 'Tsun'] >>> employee[ ] ['Anna', 'Karenina'] >>> employee[ ] ['Hans', 'Castorp'] Goal: a container of employee records indexed by employee SS# Problems: the range of SS#s is huge SS#s are not really integers Solution: the dictionary class dict >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> A dictionary contains (key, value) pairs >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee[' '] ['Yu', 'Tsun'] >>> employee[' '] ['Anna', 'Karenina'] >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee[' '] ['Yu', 'Tsun'] >>> employee[' '] ['Anna', 'Karenina'] keyvalue ' '['Anna', 'Karenina'] ' '['Yu', 'Tsun'] ' '['Hans', 'Castorp'] A key can be used as an index to access the corresponding value

Introduction to Computing Using Python Properties of dictionaries >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun']} >>> >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun']} >>> Dictionaries are not ordered Dictionaries are mutable >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun']} >>> employee[' '] = 'Holden Cafield' >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': 'Holden Cafield'} >>> >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun']} >>> employee[' '] = 'Holden Cafield' >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': 'Holden Cafield'} >>> >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun']} >>> employee[' '] = 'Holden Cafield' >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': 'Holden Cafield'} >>> employee[' '] = 'Holden Caulfield' >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': 'Holden Caulfield’} >>> employee = { ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': ['Hans', 'Castorp']} >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun']} >>> employee[' '] = 'Holden Cafield' >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': 'Holden Cafield'} >>> employee[' '] = 'Holden Caulfield' >>> employee {' ': ['Hans', 'Castorp'], ' ': ['Anna', 'Karenina'], ' ': ['Yu', 'Tsun'], ' ': 'Holden Caulfield’} Dictionaries are mutable new (key,value) pairs can be added Dictionaries are mutable new (key,value) pairs can be added the value corresponding to a key can be modified The empty dictionary is {} Dictionary keys must be immutable >>> employee = {[1,2]:1, [2,3]:3} Traceback (most recent call last): File " ", line 1, in employee = {[1,2]:1, [2,3]:3} TypeError: unhashable type: 'list' >>> employee = {[1,2]:1, [2,3]:3} Traceback (most recent call last): File " ", line 1, in employee = {[1,2]:1, [2,3]:3} TypeError: unhashable type: 'list'

Introduction to Computing Using Python Dictionary operators >>> days = {'Mo':1, 'Tu':2, 'W':3} >>> days['Mo'] 1 >>> days['Th'] = 5 >>> days {'Mo': 1, 'Tu': 2, 'Th': 5, 'W': 3} >>> days['Th'] = 4 >>> days {'Mo': 1, 'Tu': 2, 'Th': 4, 'W': 3} >>> 'Fr' in days False >>> len(days) 4 >>> days = {'Mo':1, 'Tu':2, 'W':3} >>> days['Mo'] 1 >>> days['Th'] = 5 >>> days {'Mo': 1, 'Tu': 2, 'Th': 5, 'W': 3} >>> days['Th'] = 4 >>> days {'Mo': 1, 'Tu': 2, 'Th': 4, 'W': 3} >>> 'Fr' in days False >>> len(days) 4 Class dict supports some of the same operators as class list Class dict does not support all the operators that class list supports + and * for example

Introduction to Computing Using Python Dictionary methods >>> days {'Mo': 1, 'Tu': 2, 'Th': 4, 'W': 3} >>> days.pop('Tu') 2 >>> days {'Mo': 1, 'Th': 4, 'W': 3} >>> days2 = {'Tu':2, 'Fr':5} >>> days.update(days2) >>> days {'Fr': 5, 'W': 3, 'Th': 4, 'Mo': 1, 'Tu': 2} >>> days.items() dict_items([('Fr', 5), ('W', 3), ('Th', 4), ('Mo', 1), ('Tu', 2)]) >>> days.keys() dict_keys(['Fr', 'W', 'Th', 'Mo', 'Tu']) >>> >>> vals = days.values() >>> vals dict_values([5, 3, 4, 1, 2]) >>> >>> days {'Mo': 1, 'Tu': 2, 'Th': 4, 'W': 3} >>> days.pop('Tu') 2 >>> days {'Mo': 1, 'Th': 4, 'W': 3} >>> days2 = {'Tu':2, 'Fr':5} >>> days.update(days2) >>> days {'Fr': 5, 'W': 3, 'Th': 4, 'Mo': 1, 'Tu': 2} >>> days.items() dict_items([('Fr', 5), ('W', 3), ('Th', 4), ('Mo', 1), ('Tu', 2)]) >>> days.keys() dict_keys(['Fr', 'W', 'Th', 'Mo', 'Tu']) >>> >>> vals = days.values() >>> vals dict_values([5, 3, 4, 1, 2]) >>> OperationExplanation d.items() Returns a view of the (key, value) pairs in d d.keys() Returns a view of the keys of d d.pop(key) Removes the (key, value) pair with key key from d and returns the value d.update(d2) Adds the (key, value) pairs of dictionary d2 to d d.values() Returns a view of the values of d The containers returned by d.items(), d.keys(), and d.values() (called views) can be iterated over >>> days {'Mo': 1, 'Tu': 2, 'Th': 4, 'W': 3} >>> days.pop('Tu') 2 >>> days {'Mo': 1, 'Th': 4, 'W': 3} >>> days2 = {'Tu':2, 'Fr':5} >>> days.update(days2) >>> days {'Fr': 5, 'W': 3, 'Th': 4, 'Mo': 1, 'Tu': 2} >>> days.items() dict_items([('Fr', 5), ('W', 3), ('Th', 4), ('Mo', 1), ('Tu', 2)]) >>> days.keys() dict_keys(['Fr', 'W', 'Th', 'Mo', 'Tu']) >>> >>> vals = days.values() >>> vals dict_values([5, 3, 4, 1, 2]) >>> for val in vals: print(val, end=' ') >>> >>> days {'Mo': 1, 'Tu': 2, 'Th': 4, 'W': 3} >>> days.pop('Tu') 2 >>> days {'Mo': 1, 'Th': 4, 'W': 3} >>> days2 = {'Tu':2, 'Fr':5} >>> days.update(days2) >>> days {'Fr': 5, 'W': 3, 'Th': 4, 'Mo': 1, 'Tu': 2} >>> days.items() dict_items([('Fr', 5), ('W', 3), ('Th', 4), ('Mo', 1), ('Tu', 2)]) >>> days.keys() dict_keys(['Fr', 'W', 'Th', 'Mo', 'Tu']) >>> >>> vals = days.values() >>> vals dict_values([5, 3, 4, 1, 2]) >>> for val in vals: print(val, end=' ') >>>

Introduction to Computing Using Python Dictionary vs. multi-way if statement Uses of a dictionary: container with custom indexes def complete(abbreviation): 'returns day of the week corresponding to abbreviation' if abbreviation == 'Mo': return 'Monday' elif abbreviation == 'Tu': return 'Tuesday' elif else: # abbreviation must be Su return 'Sunday' def complete(abbreviation): 'returns day of the week corresponding to abbreviation' if abbreviation == 'Mo': return 'Monday' elif abbreviation == 'Tu': return 'Tuesday' elif else: # abbreviation must be Su return 'Sunday' def complete(abbreviation): 'returns day of the week corresponding to abbreviation' days = {'Mo': 'Monday', 'Tu':'Tuesday', 'We': 'Wednesday', 'Th': 'Thursday', 'Fr': 'Friday', 'Sa': 'Saturday', 'Su':'Sunday'} return days[abbreviation] def complete(abbreviation): 'returns day of the week corresponding to abbreviation' days = {'Mo': 'Monday', 'Tu':'Tuesday', 'We': 'Wednesday', 'Th': 'Thursday', 'Fr': 'Friday', 'Sa': 'Saturday', 'Su':'Sunday'} return days[abbreviation] Uses of a dictionary: container with custom indexes alternative to the multi-way if statement

Introduction to Computing Using Python Dictionary as a container of counters >>> grades = [95, 96, 100, 85, 95, 90, 95, 100, 100] >>> frequency(grades) {96: 1, 90: 1, 100: 3, 85: 1, 95: 3} >>> >>> grades = [95, 96, 100, 85, 95, 90, 95, 100, 100] >>> frequency(grades) {96: 1, 90: 1, 100: 3, 85: 1, 95: 3} >>> Problem: computing the number of occurrences of items in a list Solution: Iterate through the list and, for each grade, increment the counter corresponding to the grade. Problems: impossible to create counters before seeing what’s in the list how to store grade counters so a counter is accessible using the corresponding grade Solution: a dictionary mapping a grade (the key) to its counter (the value) Uses of a dictionary: container with custom indexes alternative to the multi-way if statement container of counters

Introduction to Computing Using Python Dictionary as a container of counters >>> grades = [95, 96, 100, 85, 95, 90, 95, 100, 100] Problem: computing the number of occurrences of items in a list 95 1 def frequency(itemList): 'returns frequency of items in itemList' counters = {} def frequency(itemList): 'returns frequency of items in itemList' counters = {} ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ ⌃ counters def frequency(itemList): 'returns frequency of items in itemList' counters = {} for item in itemList: if item in counters: # increment item counter counters[item] += 1 else: # create item counter counters[item] = 1 return counters def frequency(itemList): 'returns frequency of items in itemList' counters = {} for item in itemList: if item in counters: # increment item counter counters[item] += 1 else: # create item counter counters[item] = 1 return counters

Introduction to Computing Using Python Exercise def numChars(filename): 'returns the number of characters in file filename' infile = open(filename, 'r') content = infile.read() infile.close() return len(content) def numChars(filename): 'returns the number of characters in file filename' infile = open(filename, 'r') content = infile.read() infile.close() return len(content) Implement function wordcount() that takes as input a text—as a string— and prints the frequency of each word in the text; assume there is no punctuation in the text. def wordCount(text): 'prints frequency of each word in text' wordList = text.split() # split text into list of words counters ={} # dictionary of counters for word in wordList: if word in counters: # counter for word exists counters[word] += 1 else: # counter for word doesn't exist counters[word] = 1 for word in counters: # print word counts if counters[word] == 1: print('{:8} appears {} time.'.format(word, counters[word])) else: print('{:8} appears {} times.'.format(word, counters[word])) def wordCount(text): 'prints frequency of each word in text' wordList = text.split() # split text into list of words counters ={} # dictionary of counters for word in wordList: if word in counters: # counter for word exists counters[word] += 1 else: # counter for word doesn't exist counters[word] = 1 for word in counters: # print word counts if counters[word] == 1: print('{:8} appears {} time.'.format(word, counters[word])) else: print('{:8} appears {} times.'.format(word, counters[word])) >>> text = 'all animals are equal but some animals are more equal than other' >>> wordCount(text) all appears 1 time. animals appears 2 times. some appears 1 time. equal appears 2 times. but appears 1 time. other appears 1 time. are appears 2 times. than appears 1 time. more appears 1 time. >>> >>> text = 'all animals are equal but some animals are more equal than other' >>> wordCount(text) all appears 1 time. animals appears 2 times. some appears 1 time. equal appears 2 times. but appears 1 time. other appears 1 time. are appears 2 times. than appears 1 time. more appears 1 time. >>>

Introduction to Computing Using Python Built-in class tuple >>> lst = ['one', 'two', 3] >>> lst[2] 3 >>> lst[2] = 'three' >>> lst ['one', 'two', 'three'] >>> tpl = ('one', 'two', 3) >>> tpl ('one', 'two', 3) >>> tpl[2] 3 >>> tpl[2] = 'three' Traceback (most recent call last): File " ", line 1, in tpl[2] = 'three' TypeError: 'tuple' object does not support item assignment >>> >>> lst = ['one', 'two', 3] >>> lst[2] 3 >>> lst[2] = 'three' >>> lst ['one', 'two', 'three'] >>> tpl = ('one', 'two', 3) >>> tpl ('one', 'two', 3) >>> tpl[2] 3 >>> tpl[2] = 'three' Traceback (most recent call last): File " ", line 1, in tpl[2] = 'three' TypeError: 'tuple' object does not support item assignment >>> The class tuple is the same as class list … except that it is immutable Why do we need it?Why do we need it? Sometimes, we need to have an “immutable list”. For example, when we need a dictionary that has lists as keys

Introduction to Computing Using Python Exercise Implement function lookup() that implements a phone book lookup application. Your function takes, as input, a dictionary representing a phone book, mappingtuples (containing the first and last name) to strings (containing phone numbers) def lookup(phonebook): '''implements interactive phone book service using the input phonebook dictionary''' while True: first = input('Enter the first name: ') last = input('Enter the last name: ') person = (first, last) # construct the key if person in phonebook: # if key is in dictionary print(phonebook[person]) # print value else: # if key not in dictionary print('The name you entered is not known.') def lookup(phonebook): '''implements interactive phone book service using the input phonebook dictionary''' while True: first = input('Enter the first name: ') last = input('Enter the last name: ') person = (first, last) # construct the key if person in phonebook: # if key is in dictionary print(phonebook[person]) # print value else: # if key not in dictionary print('The name you entered is not known.') >>> phonebook = { ('Anna','Karenina'):'(123) ', ('Yu', 'Tsun'):'(901) ', ('Hans', 'Castorp'):'(321) '} >>> lookup(phonebook) Enter the first name: Anna Enter the last name: Karenina (123) Enter the first name: >>> phonebook = { ('Anna','Karenina'):'(123) ', ('Yu', 'Tsun'):'(901) ', ('Hans', 'Castorp'):'(321) '} >>> lookup(phonebook) Enter the first name: Anna Enter the last name: Karenina (123) Enter the first name:

>>> import math >>> >>> import math >>> >>> import math >>> dir(math) ['__doc__', '__file__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc’] >>> >>> import math >>> dir(math) ['__doc__', '__file__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc’] >>> >>> import math >>> dir(math) ['__doc__', '__file__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc’] >>> math.sqrt >>> math.pi >>> import math >>> dir(math) ['__doc__', '__file__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc’] >>> math.sqrt >>> math.pi Introduction to Computing Using Python Modules, revisited When the module is executed (imported), then the module is (also) a namespace. A module is a file containing Python code. When the module is executed (imported), then the module is (also) a namespace. This namespace has a name, typically the name of the module. When the module is executed (imported), then the module is (also) a namespace. This namespace has a name, typically the name of the module. In this namespace live the names that are defined in the global scope of the module: the names of functions, values, and classes defined in the module. These names are the module’s attributes. When the module is executed (imported), then the module is (also) a namespace. This namespace has a name, typically the name of the module. In this namespace live the names that are defined in the global scope of the module: the names of functions, values, and classes defined in the module. Built-in function dir() returns the names defined in a namespace To access the imported module’s attributes, the name of the namespace must be specified

Introduction to Computing Using Python Importing a module When the Python interpreter executes an import statement, it: 1.Looks for the file corresponding to the module to be imported. 2.Runs the module’s code to create the objects defined in the module. 3.Creates a namespace where the names of these objects will live. An import statement only lists a name, the name of the module without any directory information or.py suffix. Python uses the Python search path to locate the module. The search path is a list of directories where Python looks for modules. The variable name path defined in the Standard Library module sys refers to this list. When the Python interpreter executes an import statement, it: 1.Looks for the file corresponding to the module to be imported. >>> import sys >>> sys.path ['/Users/me', '/Library/Frameworks/Python.framework/Versions/3.2/lib/python32.zip',... '/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages'] >>> >>> import sys >>> sys.path ['/Users/me', '/Library/Frameworks/Python.framework/Versions/3.2/lib/python32.zip',... '/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages'] >>> current working directoryStandard Library folders

>>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import example Traceback (most recent call last): File " ", line 1, in import example ImportError: No module named example >>> >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import example Traceback (most recent call last): File " ", line 1, in import example ImportError: No module named example >>> >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> Introduction to Computing Using Python The Python search path Suppose we want to import module example stored in folder /Users/me that is not in list sys.path >>> ================ RESTART ================ >>> >>> ================ RESTART ================ >>> >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import example Traceback (most recent call last): File " ", line 1, in import example ImportError: No module named example >>> import sys >>> sys.path.append('/Users/me') >>> import example >>> example.f >>> example.x 0 >>> >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import example Traceback (most recent call last): File " ", line 1, in import example ImportError: No module named example >>> import sys >>> sys.path.append('/Users/me') >>> import example >>> example.f >>> example.x 0 >>> >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import example Traceback (most recent call last): File " ", line 1, in import example ImportError: No module named example >>> import sys >>> sys.path.append('/Users/me') >>> import example >>> example.f >>> example.x 0 >>> dir() ['__builtins__', '__doc__', '__name__', '__package__', 'example', 'sys’] >>> ================ RESTART ================ >>> dir() ['__builtins__', '__doc__', '__name__', '__package__'] >>> import example Traceback (most recent call last): File " ", line 1, in import example ImportError: No module named example >>> import sys >>> sys.path.append('/Users/me') >>> import example >>> example.f >>> example.x 0 >>> dir() ['__builtins__', '__doc__', '__name__', '__package__', 'example', 'sys’] By just adding folder /Users/me to the search path, module example can be imported When called without an argument, function dir() returns the names in the top-level module the shell, in this case. 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var names in the shell namespace; note that example is not in no folder in the Python search path contains module example

Introduction to Computing Using Python Three ways to import module attributes 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var example.py namespace __main__ >>> f module example example f() 0 0 gx g() 1. Import the (name of the) module >>> import example >>> >>> import example >>> >>> import example >>> example.x 0 >>> example.f >>> example.f() Executing f() >>> >>> import example >>> example.x 0 >>> example.f >>> example.f() Executing f() >>>

Introduction to Computing Using Python Three ways to import module attributes 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var example.py namespace __main__ >>> f module example f f() 0 0 gx g() 2. Import specific module attributes >>> from example import f >>> >>> from example import f >>> >>> from example import f >>> f() Executing f() >>> x Traceback (most recent call last): File " ", line 1, in x NameError: name 'x' is not defined >>> >>> from example import f >>> f() Executing f() >>> x Traceback (most recent call last): File " ", line 1, in x NameError: name 'x' is not defined >>>

Introduction to Computing Using Python Three ways to import module attributes 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var 'an example module' def f(): 'function f' print('Executing f()') def g(): 'function g' print('Executing g()') x = 0 # global var example.py namespace __main__ >>> 3. Import all module attributes >>> from example import * >>> >>> from example import * >>> >>> from example import * >>> f() Executing f() >>> g() Executing g() >>> x 0 >>> >>> from example import * >>> f() Executing f() >>> g() Executing g() >>> x 0 >>> f module example f f() 0 0 gx g() g x

Introduction to Computing Using Python A class is a namespace >>> list.pop >>> list.sort >>> >>> list.pop >>> list.sort >>> __add__ namespace list __add__() sort() count x count() pop pop() A class is really a namespace The name of this namespace is the name of the class The names defined in this namespace are the class attributes (e.g., class methods)... A class is really a namespace The name of this namespace is the name of the class The names defined in this namespace are the class attributes (e.g., class methods) The class attributes can be accessed using the standard namespace notation Function dir() can be used to list the class attributes >>> list.pop >>> list.sort >>> dir(list) ['__add__', '__class__',... 'index', 'insert', 'pop', 'remove', 'reverse', 'sort'] >>> list.pop >>> list.sort >>> dir(list) ['__add__', '__class__',... 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

A class method is really a function defined in the class namespace; when Python executes it first translates it to and actually executes this last statement Introduction to Computing Using Python Class methods >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> __add__ namespace list __add__() sort() count x count() pop pop()... >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> lst.append(6) >>> lst [1, 2, 3, 7, 8, 9, 6] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> lst.append(6) >>> lst [1, 2, 3, 7, 8, 9, 6] >>> >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> lst.append(6) >>> lst [1, 2, 3, 7, 8, 9, 6] >>> list.append(lst, 5) >>> lst [1, 2, 3, 7, 8, 9, 6, 5] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> lst.sort() >>> lst [1, 2, 3, 7, 8, 9] >>> lst = [9, 1, 8, 2, 7, 3] >>> lst [9, 1, 8, 2, 7, 3] >>> list.sort(lst) >>> lst [1, 2, 3, 7, 8, 9] >>> lst.append(6) >>> lst [1, 2, 3, 7, 8, 9, 6] >>> list.append(lst, 5) >>> lst [1, 2, 3, 7, 8, 9, 6, 5] lst.sort() list.sort(lst) lst.append(6) instance.method(arg1, arg2, …) list.append(lst, 6) class.method(instance, arg1, arg2, …) The function has an extra argument, which is the object invoking the method

Rewrite the below Python statement so that instead of making the usual method invocations you use the notation Introduction to Computing Using Python Exercise >>> s = 'hello' >>> s = 'ACM' >>> s.lower() 'acm' >>> s.find('C') 1 >>> s.replace('AC', 'IB') 'IBM' >>> s = 'hello' >>> s = 'ACM' >>> s.lower() 'acm' >>> s.find('C') 1 >>> s.replace('AC', 'IB') 'IBM' lst.sort() list.sort(lst) lst.append(6) instance.method(arg1, arg2, …) list.append(lst, 6) class.method(instance, arg1, arg2, …) >>> s = 'ACM' >>> str.lower(s) 'acm' >>> str.find(s, 'C') 1 >>> str.replace(s, 'AC', 'IB') 'IBM' >>> >>> s = 'ACM' >>> str.lower(s) 'acm' >>> str.find(s, 'C') 1 >>> str.replace(s, 'AC', 'IB') 'IBM' >>>