When framing if condition for 'add_length' , isinstance has 2nd parameter 'length' but in the case of 'add_inches' the 2nd parameter is given int(integer) . I could not understand this part .why can't they both be int(integer). Help is appreciated !
class Length:
def __init__(self, feet, inches):
self.feet = feet
self.inches = inches
def __str__(self):
return f'{self.feet} {self.inches}'
def __add__(self, other):
if isinstance(other, Length):
return self.add_length(other)
if isinstance(other, int):
return self.add_inches(other)
else:
return NotImplemented
def __radd__(self, other):
return self.__add__(other)
def add_length(self, L):
f = self.feet + L.feet
i = self.inches + L.inches
if i >= 12:
i = i - 12
f += 1
return Length(f, i)
def add_inches(self, inches):
f = self.feet + inches // 12
i = self.inches + inches % 12
if i >= 12:
i = i - 12
f += 1
return Length(f, i)
length1 = Length(2, 10)
length2 = Length(3, 5)
print(length1 + length2)
print(length1 + 2`
print(length1 + 20)
print(20 + length1)
The first condition is checking for the scenario when two length objects are added together:
length1 = Length(2, 10)
length2 = Length(3, 5)
print(length1 + length2)
The second condition is checking for the scenario when an integer is added to a length.
print(length1 + 2)
print(length1 + 20)
The conditional calls two different methods add_length and add_inches because of how the data needs to be accessed. That is, for add_length it accessed via properties of the object (L). For add_inches it is accessed from the integer (inches).
From my understanding, this is simply the way this class is designed.
You can either add two objects from the length class together (this is the first isinstance) or you can add an integer in inches to the length (this is the second isinstance).
Related
I want to create a LimitedPrecisionFloat class that would allow me to store a float with n-digits (I don't want to round the number, just cut the remaining digits). This is how I would like it to behave:
a = LimitedPrecisionFloat(3.45678, ndigits=3)
print(a) # 3.456
a += 0.11199
print(a) # 3.567
a -= 0.567999
print(a) # 3 (or 3.0 or 3.000)
print(a + 1.9999) # 4.999
# same with other arithmetic operators, ie.
print(LimitedPrecisionFloat(1.11111 * 9.0, 3) # 9.999
...
What I currently have is:
def round_down(x:float, ndigits:int):
str_x = str(x)
int_part = str(int(x))
fraction_part = str_x[str_x.find('.') + 1:]
fraction_part = fraction_part[:ndigits]
return float(int_part + '.' + fraction_part)
class LimitedPrecisionFloat(float):
def __new__(cls, x, ndigits:int):
return super(LimitedPrecisionFloat, cls).__new__(cls, round_down(x, ndigits))
def __init__(self, x, ndigits: int):
super().__init__()
self.ndigits = ndigits
def __add__(self, other):
return round_down(float(self) + other, ndigits=self.ndigits)
def __sub__(self, other):
return round_down(float(self) - other, ndigits=self.ndigits)
# other operators
However, this will not work, because whenever __add__ (or any other operator) is called, it returns float and the precision is back in the number. So when I tried doing something like this:
def __add__(self, other):
return LimitedPrecisionFloat(float(self) + other, ndigits=self.ndigits)
But then I got the max recursion depth error.
Because of that, I also don't have a clue on how to implement augmented arithmetic assignments, like __iadd__.
I tried :
def fibonnaci(n):
total_call = 0
if n ==0 or n == 1:
return 1
else:
if n== 2 or n == 1:
total_call +=0
else:
total_call +=2
return fibonnaci(n - 1) + fibonnaci(n - 2), total_call
n = 8
print(fibonnaci(n))
but I got a error:
TypeError: can only concatenate tuple (not "int") to tuple
How to display the number of calls for fibonnaci?
In your return statement the result of both fibonnaci(n - 1) and fibonnaci(n - 2) could be a tuple (argument > 1), or a single integer (argument <= 1) thus + means concatenation when the first one is a tuple. But when n == 3 in return fibonacci(n - 1) + fibonacci(n - 2), total_call fibonacci(2) is a tuple ((2, total_call)), while fibonacci(1) is an integer (1). So you want to concatenate a tuple with with an integer, which is impossible.
Using Decorators
Using Function Attributes
Reference
Code
def call_counter(func):
" Does the call count for any function "
def helper(x):
helper.calls += 1
return func(x)
helper.calls = 0
return helper
#call_counter
def fib(n):
if n ==0 or n == 1:
return 1
return fib(n - 1) + fib(n - 2)
Usage
fib(5)
print(fib.calls)
fib(10)
print(fib.calls) # Keeps running total so will be from previous
# fib(5) plus current fib(10)
# To reset counter
fib.calls = 0
Using Class
Reference
Code
class countCalls(object):
"""Decorator that keeps track of the number of times a function is called.
::
>>> #countCalls
... def foo():
... return "spam"
...
>>> for _ in range(10)
... foo()
...
>>> foo.count()
10
>>> countCalls.counts()
{'foo': 10}
Found in the Pythod Decorator Library from http://wiki.python.org/moin web site.
"""
instances = {}
def __init__(self, func):
self.func = func
self.numcalls = 0
countCalls.instances[func] = self
def __call__(self, *args, **kwargs):
self.numcalls += 1
return self.func(*args, **kwargs)
def count(self):
"Return the number of times this function was called."
return countCalls.instances[self.func].numcalls
#staticmethod
def counts():
"Return a dict of {function: # of calls} for all registered functions."
return dict([(func.__name__, countCalls.instances[func].numcalls) for func in countCalls.instances])
#countCalls
def fib(n):
if n ==0 or n == 1:
return 1
return fib(n - 1) + fib(n - 2)
Example
print(fib(3)) # Output 3
print(fib.count()) # Output 5
Advantage
Allows obtaining counts of all registered functions (i.e. registered by using decorator)
#countCalls
def f(n):
pass # dummy function
#countCalls
def g(n):
pass # dummy function
for i in range(5):
f(i)
for i in range(10):
g(i)
print(countCalls.counts())
# Outputs: {'f': 5, 'g': 10}
def fib(n):
if n <= 1:
return n, 1
fib_one = fib(n - 1)
fib_two = fib(n - 2)
#Return the result and the number of function calls (+ 1 for the current call)
return fib_one[0] + fib_two[0], fib_one[1] + fib_two[1] + 1
if __name__ == '__main__':
number_of_function_calls = fib(4)[1]
Fib(4) should return 9, which it does
fib(4)
fib(3) fib(2)
fib(2) fib(1) fib(1) fib(0)
fib(1) fib(0)
The problem is "obvious", if you bother to trace the values you're using:
return fibonnaci(n - 1) + fibonnaci(n - 2), total_call
When n is 3, this tries to "add" fibonnaci(2), a tuple, and fibonnaci(1), the integer 1. This is not a legal operation. You need to regularize your return values. You can't magically return the value alone (not the count) when that's what you want; you have to explicitly program the difference: dismember the tuple and add the component values.
Start with your base case being
return 1, 0
Your recursion case needs to add the components. Implementation is left s an exercise for the student.
Here's another answer using a decorator. The advantage of using a decorator is that the base function fib does not need to change. That means the total_count code and multiple return values can be discarded from your original attempt -
#counter(model = fib_result)
def fib(n = 0):
if n < 2:
return n
else:
return fib(n - 1) + fib(n - 2)
Our decorator counter accepts a model so we can respond to the behavior of the decorated function. Our decorated fib will return a fib_result such as { result: ?, count: ? }. That means we also need to handle fib(?) + fib(?) which is why we also defined __add__ -
class fib_result:
def __init__(self, result, count = 0):
if isinstance(result, fib_result):
self.result = result.result
self.count = result.count + count
else:
self.result = result
self.count = count
def __add__(a, b):
return fib_result(a.result + b.result, a.count + b.count)
As you can see, this fib_result is specific to counting fib calls. A different model may be required for counting other recursive functions that return other types of results.
All that's left now is to define our generic counter decorator. Our decorator takes arguments and returns a new decorator, lambda f: ..., which simply captures the passed arguments, lambda *args: ..., and constructs a new model with the result of f(*args) and a base count of 1 -
def counter(model = tuple):
return lambda f: lambda *args: model(f(*args), 1)
Here's how the complete program works -
r = fib(4)
print(f"answer: {r.result}, recurs: {r.count}")
# answer: 3, recurs: 9
r = fib(10)
print(f"answer: {r.result}, recurs: {r.count}")
# answer: 55, recurs: 177
I am currently working on creating a Polynomial class that includes add , mul and eval methods. I'm currently stuck on the addition portion, if someone could give me some help on how to get that figured out that would be greatly appreciated. Everything currently works without errors but when I do p3 = p1 + p2 and I print p3 I get back the two lists together. Any feedback would be greatly appreciated.
class Polynomial(object):
def __init__(self, *coeffs, num = 0):
self.coeffs = list(coeffs) # turned into a list
assert (type(num) is type(1))
self.num = num
# Needs to be operator overload
'''
def __mul__(self, other):
'''
def __eval__(self, other, coeff, x):
result = coeff[-1]
for i in range(-2, -len(coeff)-1, -1):
result = result * x + coeff[i]
return result
def __add__(self, other):
assert type(other) is Polynomial
num = self.coeffs + other.coeffs
return Polynomial(num)
def __sub__(self, other):
assert type(other) is Polynomial
num = self.coeffs - other.coeffs
return Polynomial(num)
def __represntation__(self):
return "Polynomial" + str(self.coeffs)
def __str__(self):
rep = ""
degree = len(self.coeffs) - 1
rep += str(self.coeffs[0]) + "x^" + str(degree)
for i in range(1, len(self.coeffs)-1):
coeff = self.coeffs[i]
if coeff < 0:
rep += " - " + str(-coeff) + "x^" + str(degree - i)
else:
rep += " + " + str(coeff) + "x^" + str(degree - i)
if self.coeffs[-1] < 0:
rep += " - " + str(-self.coeffs[-1])
else:
rep += " + " + str(self.coeffs[-1])
return rep
You cannot directly add two lists.
def __add__(self, other):
assert type(other) is Polynomial
assert len(self.coeffs) != len(other.coeffs)
new_ceffs = [item1 + item2 for (item1, item2) in zip(self.coeffs, other.coeffs)]
return Polynomial(new_ceffs)
The problem is here:
num = self.coeffs + other.coeffs
Adding one list to another list concatenates them. To simply add corresponding elements to each other, you'd want to do
from itertools import zip_longest
...
num = [a + b for (a, b) in zip_longest(self.coeffs, other.coeffs, fillvalue=0)]
We use zip_longest() instead of the more generic zip() because one polynomial is possibly longer than the other and we don't want to ruin it. Either one of them will group together the corresponding elements so that we can easily add them and make a list of those.
You would do something similar for subtraction.
you should reverse the order of coefficients passed to your constructor so that indexes in the self.coeffs list correspond to the exponents. This would simplify the rest of your code and allow you to use zip_longest for additions and subtractions.
When you get to other operations however, I think you will realize that your internal structure would be easier to manage if it was a dictionary. A dictionary is more permissive of missing entries thus avoiding preoccupations of allocating spaces for new indexes.
class Polynomial(object):
def __init__(self, *coeffs):
self.coeffs = {exp:c for exp,c in enumerate(coeffs[::-1])}
def __add__(self, other):
assert type(other) is Polynomial
result = Polynomial(0)
result.coeffs = {**self.coeffs}
for exp,c in other.coeffs.items():
result.coeffs[exp] = result.coeffs.get(exp,0) + c
return result
def __sub__(self, other):
assert type(other) is Polynomial
result = Polynomial(0)
result.coeffs = {**self.coeffs}
for exp,c in other.coeffs.items():
result.coeffs[exp] = result.coeffs.get(exp,0) - c
return result
def __mul__(self, other):
assert type(other) is Polynomial
result = Polynomial(0)
for exp1,c1 in self.coeffs.items():
for exp2,c2 in other.coeffs.items():
result.coeffs[exp1+exp2] = result.coeffs.get(exp1+exp2,0) + c1*c2
return result
def __representation__(self):
return "Polynomial" + str(self.coeffs)
def __str__(self):
result = [""]+[f"{c}x^{i}" for i,c in sorted(self.coeffs.items()) if c]+[""]
result = "+".join(reversed(result))
result = result.replace("+1x","+x")
result = result.replace("-1x","-x")
result = result.replace("x^0","")
result = result.replace("x^1+","x+")
result = result.replace("+-","-")
result = result.strip("+")
result = result.replace("+"," + ")
result = result[:1]+result[1:].replace("-"," - ")
return result.strip()
I am trying to print out a succession of coefficients of a simple polynomial using *args
I roughly understand how *args works and I know how to use a simple loop to print out each coefficient, but in a __repr__ function that is supposed to return only one thing as the return value of function, I am confused how to do this...
class Polynomial:
def __init__(self, *coefficients):
self.coeffs = coefficients
def __repr__(self):
return "Polynomial( {} )".format(self.coeffs)
p1 = Polynomial(1, 2, 3)
p2 = Polynomial(3, 4, 3)
print(p1) # Polynomial( (1, 2, 3) )
print(p2) # Polynomial( (3, 4, 3) )
The outcome of print is what comes after the comments obviously, though what I am after is this format:
1x^2 + 2x + 3
3x^2 + 4x + 3
I have tried the following, but I cannot seem to get it right.
def __repr__(self):
# return "Polynomial( {}x^2 + {}x + {} )".format(self.coeffs)
# return "Polynomial( {0}x^2 + {1}x + {2} )".format(self.coeffs)
# return "Polynomial( {0}x^2 + {1}x + {2} )".format( enumerate(self.coeffs) )
Is there a neat way of doing this without having to loop through the args elements and all in one go within the return statement?
You can use the * syntax in __repr__ as well:
def __repr__(self):
return "Polynomial( {}x^2 + {}x + {} )".format(*self.coeffs)
However, if you want to have __repr__ adjust to the degree of the polynomial, you probably need a loop of some sort:
def __repr__(self):
degree = len(self.coeffs) - 1
polystr = ' + '.join('{}x^{}'.format(term, degree-i)
for i, term in enumerate(self.coeffs))
return "Polynomial( {} )".format(polystr)
Try this (I'm taking the coefficients as a list):
exp = len(self.coeffs)
i = 0
s = ""
while exp > -1:
s += str(coeffs[i]) + "x^" + str(exp) + " "
exp -= -1
i += 1
return s
Or, if you'll always have 2 as the highest exponent, you could use * to select all of the coeffs, as in .format(*self.coeffs).
I'm trying to combine two applications for visualising binaries, binvis and droidcolors. Since droidcolors is in C, I'm trying to make binvis replicate the functionality offered by droidcolors.
Here are the relevant snippets from the code that I've written so far. The complete file is here: https://pastebin.com/0C7fu9W2.
class _Color:
def __init__(self, data, **kwargs):
self.data = data
for key, value in kwargs.items():
setattr(self, key, value)
s = list(set(data))
s.sort()
self.symbol_map = {v : i for (i, v) in enumerate(s)}
def __len__(self):
return len(self.data)
def point(self, x):
if hasattr(self, 'class_defs') and (self.class_defs[0] <= x <= self.class_defs[1]):
return self.return_droidcolors_classdefs(x)
elif hasattr(self, 'dat') and (self.dat[0] <= x <= self.dat[1]):
return self.return_droidcolors_data(x)
elif hasattr(self, 'field_ids') and (self.field_ids[0] <= x <= self.field_ids[1]):
return self.return_droidcolors_field_ids(x)
elif hasattr(self, 'header') and (self.header[0] <= x <= self.header[1]):
return self.return_droidcolors_header(x)
elif hasattr(self, 'links') and (self.links[0] <= x <= self.links[1]):
return self.return_droidcolors_links(x)
elif hasattr(self, 'proto_ids') and (self.proto_ids[0] <= x <= self.proto_ids[1]):
return self.return_droidcolors_proto_ids(x)
elif hasattr(self, 'method_ids') and (self.method_ids[0] <= x <= self.method_ids[1]):
return self.return_droidcolors_method_ids(x)
elif hasattr(self, 'string_ids') and (self.string_ids[0] <= x <= self.string_ids[1]):
return self.return_droidcolors_string_ids(x)
elif hasattr(self, 'type_ids') and (self.type_ids[0] <= x <= self.type_ids[1]):
return self.return_droidcolors_type_ids(x)
elif hasattr(self, 'block') and (self.block[0] <= x <= self.block[1]):
return self.block[2]
else:
return self.getPoint(x)
# --- snip ---
class ColorDroidColors(_Color):
def getPoint(self, x):
return [0, 0, 0]
# --- snip ---
dex_handle = Dexparser(args[0])
dex_header_info = dex_handle.header_info()
dex_class_defs = (dex_header_info['class_defs_off'], dex_header_info['class_defs_off'] + (64 * dex_header_info['class_defs_size']) - 1)
dex_data = (dex_header_info['data_off'], dex_header_info['data_off'] + dex_header_info['data_size'] - 1)
dex_field_ids = (dex_header_info['field_ids_off'], dex_header_info['field_ids_off'] + (8 * dex_header_info['field_ids_size']) - 1)
dex_header = (0x0, dex_header_info['header_size'] - 1)
dex_links = (link_off, link_off + dex_header_info['link_size'] - 1)
dex_proto_ids = (dex_header_info['proto_ids_off'], dex_header_info['proto_ids_off'] + (12 * dex_header_info['proto_ids_size']) - 1)
dex_method_ids = (dex_header_info['method_ids_off'], dex_header_info['method_ids_off'] + (8 * dex_header_info['method_ids_size']) - 1)
dex_string_ids = (dex_header_info['string_ids_off'], dex_header_info['string_ids_off'] + (4 * (dex_header_info['string_ids_size']) - 1))
dex_type_ids = (dex_header_info['type_ids_off'], dex_header_info['type_ids_off'] + (4 * dex_header_info['type_ids_size']) - 1)
kwarg_dict = {
"class_defs": dex_class_defs,
"dat": dex_data,
"field_ids": dex_field_ids,
"header": dex_header,
"links": dex_links,
"proto_ids": dex_proto_ids,
"method_ids": dex_method_ids,
"string_ids": dex_string_ids,
"type_ids": dex_type_ids,
}
for i, item in enumerate(dex_handle.protoids_list()):
if item[2]:
kwarg_dict['dex_proto_params_' + str(i)] = (item[2], (0x0 + item[2]) * 4 + 4)
csource = ColorDroidColors(
d,
**kwarg_dict
)
I'm basically passing 10000+ kwargs to a method, and require a way to test within the method if a kwarg exists and depending on the same, to return some value. All the kwargs have a particular prefix, followed by sequential numbers starting from 1. I tried using a for loop, but that slowed the program down to a crawl.
Could anyone please suggest me a way out?
Use getattr() and a list of attributes to test:
attrs = ['class_defs', 'dat', 'field_ids', ..., 'block']
for name in attrs:
value = getattr(self, name, None)
if value is not None and value[0] <= x <= value[1]
if name != 'block':
method_name = 'return_droidcolors_' + name
return getattr(self, method_name)(x)
else:
return value[2]
# none of the attributes matched
return self.getPoint(x)
Note that in your __init__ method, you could just use self.__dict__.update(kwargs) rather than loop through the dictionary and call setattr() each time.