Intro to Programming with Python Practical Session 12

Intro to Programming with Python Practical Session #12 Summary Questions 1

Q 1 – Partition 2

Q 1 – Partition • (? ) 4

Q 1 – Solution def P(l, s 1=0, s 2=0): if not l: #if l has no objects return s 1 == s 2 return P(l[1: ], s 1+l[0], s 2) or P(l[1: ], s 1, s 2+l[0]) 5

Q 1 – With memoization def P(l, s 1=0, s 2=0, mem=None): if not l: return s 1 == s 2 if not mem: #if mem hasn’t been set yet mem = {} key = (len(l), s 1, s 2) #can we also use (l, s 1, s 2)? if key not in mem: mem[key] = P(l[1: ], s 1+l[0], s 2, mem) or P(l[1: ], s 1, s 2+l[0], mem) return mem[key] 6

Q 2 – Least Used Dictionary 7

Q 2 – code class LUD: def __init__(self, memory_size): if memory_size < 1: #TODO raise Value. Error('Error memory size') self. memory_size = memory_size self. data = {} Called when len() self. usage = {} is applied to LUD def __len__(self): return len(self. data) #TODO Called when key in LUD expression is evaluated def __contains__(self, key): return key in self. data #TODO 10

Q 2 – code def extract_value(key_value): return key_value[1] class LUD: . . . Outside class definition. Doesn’t get “self” def get(self, key): val = self. data. get(key) #TODO if val != None: self. usage[key] += 1 return val def put(self, key, value): if len(self) == self. memory_size and key not in in self: #TODO mkey, mval = min(self. usage. items(), key=extract_value) self. data. pop(mkey) self. usage. pop(mkey) self. data[key] = value self. usage[key] = 0 11

Q 3 – Binary Tree 12

Q 3 – Binary trees 13

Q 3 – Binary trees def is_leaf(tree): #TODO return not tree[1] and not tree[2] #another option def is_leaf(tree): return len(tree[1])==0 and / len(tree[2])==0 14

Q 3 – Binary trees Ideas? 15

Q 3 – Binary trees def is_binary(tree): if not isinstance(tree, list): #TODO return False if not tree: #Empty list is legal return True if len(tree) != 3: return False if not isinstance(tree[0], int): return False return is_binary(tree[1]) and is_binary(tree[2]) When shall we return False? 16

Q 3 – Binary trees def opt_tree(tree, f = min): If is_leaf(tree): #TODO return tree[0] if tree[1]: tree_1_result = opt_tree(tree[1] , f) if tree[2]: tree_2_result = opt_tree(tree[2] , f) result = f(tree[0], tree_1_result, tree_2_result) return result 17

Q 3 – Binary trees Ideas? 18

Q 3 – Binary trees def count_good(tree): if is_leaf(tree): #TODO return 1 is_good = True num_good_sons = 0 if tree[1]: num_good_sons += count_good(tree[1]) is_good = tree[0] >= opt_tree(tree[1], max) if tree[2]: num_good_sons += count_good(tree[2]) is_good = is_good and tree[0] <= opt_tree(tree[2], min) return num_good_sons + is_good #How much is 17+True? 19

Q 4 – Files & Folders 20

Q 4 – Files and folders המקבלת תיקייה ומחזירה רשימה list_files • בסעיף זה נממש פונקציה (((. . . ) המכילה את כל הקבצים )כולל קבצים הנמצאים בתתי)תתי . ( תיקיות . • אין חשיבות לסדר ההחזרה def list_files(folder): result = [] #TODO for item in folder[1: ]: [1: ] if isinstance(item, str): result. append(item) else: result. extend(list_files(item)) return result 22

Q 4 – Files and folders def exist(folder, path): #TODO if len(path) == 1: return search_file(folder, path[0]) for item in folder[1: ]: if isinstance(item, list) and item[0] == path[0]: return exist(item, path[1: ]) return False # file not found 25

Q 5 – Polynomials 26

Q 5 – Polynomials construction : • נתונים הפולינומים : נממש מתודת בנאי class Polynomial: def __init__(self, coefficients_list = []): self. coef = coefficients_list #TODO 28

Q 5 – Polynomials addition נתונים ע"י c(x)=a(x)+b(x) מקדמי הפולינום : • תזכורת class Polynomial: . . . def __add__(self, other): res = [0] * max(len(self. coef), len(other. coef)) #TODO for i in range(len(self. coef)): res[i] += self. coef[i] for i in range(len(other. coef)): res[i] += other. coef[i] return Polynomial(res) 29

Q 5 – Polynomials multiplication נתונים ע"י c(x)=a(x)*b(x) מקדמי הפולינום : • תזכורת class Polynomial: . . . def __mul__(self, other): res = [0] * (len(self. coef)+len(other. coef)-1) #TODO for i in range(len(self. coef)): for j in range(len(other. coef)): res[i+j] += self. coef[i] * other. coef[j] return Polynomial(res) 30

Polynomials with numpy >>> import numpy. polynomial as poly >>> #p 1 = 6 -5 x+x^2 >>> p 1 = poly. Polynomial([6, -5, 1]) >>> p 1. coef array([ 6. , -5. , 1. ]) >>> p 1. roots() array([ 2. , 3. ]) >>> p 1(3) #calculates the value of the polynom for x=3 0. 0 >>> p 2 = poly. Polynomial([1, 0, 2]) #p 2=1+2 x^2 >>> (p 1+p 2). coef array([ 7. , -5. , 3. ]) Full documentation: http: //docs. scipy. org/doc/numpy/reference/routines. polynomial. ht 31 ml

Q 6 – Bookworm 32

Q 6 – Bookworm. • בשאלה זו נממש תוכנה לניהול ספרייה : הכוללת Book • תחילה נממש את המחלקה (title) שם הספר (author) שם הסופר (pages) מספר דפים . ספרות 10 בן tuple- נתון כ ISBN קוד • • class Book: def __init__(self, title, author, pages, isbn): self. title = title self. author = author self. pages = pages self. isbn = isbn 33

Q 8 – Bookworm : • נוסיף פונקציה שתוודא את תקינות הקוד class Book: . . . def isbn_is_valid(self): if len(self. isbn) != 10: return False res = 0 for i in range(9): res += self. isbn[i] * (10 -i) return res%10 == self. isbn[9] : • נוסיף בדיקה בסוף הבנאי # at the end of __init__ if not self. isbn_is_valid(): raise Value. Error('Illegal ISBN code') 35

Q 8 – Bookworm יחזיק מיפוי Library כל אובייקט מסוג. Library • כעת נממש את המחלקה . לספרים ISBN מקודי • מחלקה זו תאפשר הוספת ספר יחיד לספרייה או את כל הספרים מספרייה . ( אחרת )ועבור קלט אחר תזרוק שגיאה Note that Book class Library: references are def __init__(self): copied between self. lib = {} libraries, and not def add_books(self, other): the Book’s data if isinstance(other, Library): self. lib. update(other. lib) elif isinstance(other, Book): self. lib[other. isbn] = other else: raise Type. Error('Can not add to Library. ') 36

Exam 37