I'm fairly new to python and understand that recursion is an important concept to grasp. I've been dabbling with various scripts to exercise my knowledge and have come up with the following script to simulate a lottery draw, where you simply draw six from 49 numbers and compare them with another six to see if you've won. I'm struggling though with the recursive function taking the value of another function.
I'm sure it's going to be straightforwardish, but cannot fathom it myself.
Here's my code so far:
from random import randint
def drawSix():
six = []
while len(six) < 6:
a = randint(1,49)
if a not in six:
six.append(a)
return sorted(six)
def lottery(draw,ticket):
if draw == ticket:
return 'win'
return lottery(drawSix(),drawSix())
I call the function with lottery(drawSix(),drawSix())
and get the following recursively.
Traceback (most recent call last):
File "<pyshell#0>", line 1, in <module>
lottery(drawSix(),drawSix())
File "/Users/johnhopkins/Desktop/lottery.py", line 14, in lottery
return lottery(drawSix(),drawSix())
def lottery(draw,ticket):
if draw == ticket:
return 'win'
return lottery(drawSix(),drawSix())
The odds of you actually generating two identical tickets are quite large, well over 1000 which is the maximum stack size of Python.
You need to either do this iteratively to avoid blowing your stack.
def lottery(draw,ticket):
while draw != ticket:
draw, ticket = drawSix(), drawSix()
return "win"
Note this has a very ugly O(n) of O(inf) you could end up running this forever if you were unlucky and still not finding a winning pair
Well, your question has has been answered, but I would suggest changing your drawSix function. As it is now, it could technically run forever. random has a sample method to generate unique numbers.
def drawSix():
return sorted(random.sample(range(1, 50), 6))
Yes - the lottery function will keep on calling itself, each time putting a new version of itself onto the call stack, going deeper and deeper into itself until there are two matching numbers.
This can take a long time, and Python will eventually say "oi! stop it!" and crash.
Some programming languages have a feature called 'tail call optimisation', which means if you try to return the result of the same function, instead of making a new call to the function inside the current one, it simply replaces itself in the stack.
Python doesn't do that.
def lottery():
while (drawSix() != drawSix()):
continue
return 'win!'
will have the same effect as your recursive version, but won't die with recursion errors.
You have not made any programming mistakes. However, the probility of winning the lottery is very small, so you need to generate a lot. Easy recursion add something to the stack.
Number of lotto tickets can be found by the formula for combinations with repetition:
(49+6-1)! / (6! * (49-1)!) = 25827165
This is a lot... Decrease the number 6 or 49, add some debugging lines and you'll see that the code works fine!
Related
I am very new to python, and am running into an issue I don't fully understand. I am trying to get a random variable to run multiple times, but for some reason it just returns the same random value x times.
I am not entirely certain what to try aside from the code I have already done.
lowTreasureList = "50 gold", "Healing Potion", "10x Magic Arrows", "+1 Magic Weapon"
def ranLowLoot(lowLootGiven):
# This function returns a random string from the passed list of strings.
lootIndex = random.randint(0, len(lowLootGiven) - 1)
return lowLootGiven[lootIndex]
lowLoot = ranLowLoot(lowTreasureList)
treasureSelection = int(input())
if treasureSelection == 1:
numLowTreasure = int(input('How many treasures? '))
for i in range(numLowTreasure):
ranLowLoot(lowTreasureList)
print(lowLoot)
When I do this I get the same random treasure (numLowTreasure) times, but I am trying to get it to select a new random treasure each time.
If you haven't already, it will help to read the documentation on the random module.
There are three alternatives to random.randint that are more suited to your purpose:
random.randrange(start, stop, [step]): step is optional and defaults to one. This will save you the len(...) - 1 you are using to get lootIndex, since stop is an exclusive bound.
random.randrange(stop): uses a default start of zero and default step of 1, which will save you passing 0 as your start index.
random.choice(seq): you can pass your function's parameter lowLootGiven to this as seq, which will save you from using indices and writing your own function entirely.
As for why you're getting the repeated treasure, that's because you aren't updating your variable lowLoot in your for loop. You should write:
for i in range(numLowTreasure):
lowLoot = ranLowLoot(lowTreasureList)
print(lowLoot)
Last thing I want to say is that python is nice for writing simple things quickly. Even if there was some bigger context that you were writing this code in, I might have written it like this:
lowTreasureList = ("50 gold", "Healing Potion", "10x Magic Arrows", "+1 Magic Weapon")
if int(input()) == 1:
for i in range(int(input('How many treasures? '))):
print(random.choice(lowTreasureList))
Using the round parentheses around the tuple declaration like I did isn't necessary in this case, but I like to use it because if you want to make the tuple declaration span multiple lines, it won't work without them.
Reading documentation on standard libraries is something I almost always find helpful. I think Python's documentation is great, and if it's bit too much to digest early on, I found tutorialspoint to be a good place to start.
The problem is that in the main loop you are discarding the result of the call to ranLowLoot(). As a minimal fix, in the main loop assign the result of that function call. Use:
lowLoot = ranLowLoot(lowTreasureList)
rather than simply:
ranLowLoot(lowTreasureList)
As a better fix, ditch your function completely and just use random.choice() (which does what you are trying to do, with much less fuss):
import random
lowTreasureList = ["50 gold", "Healing Potion", "10x Magic Arrows", "+1 Magic Weapon"]
treasureSelection = int(input())
if treasureSelection == 1:
numLowTreasure = int(input('How many treasures? '))
for i in range(numLowTreasure):
lowLoot = random.choice(lowTreasureList)
print(lowLoot)
for an assignment we needed to make a function that flipped a coin and another to flip it 100 times. I was able to make a function that flipped a coin, but got stuck when trying to call it a 100 times with another function. This is what I have right now:
import random
def TC():
face = random.randint(0,1)
if face == 1:
return "head"
else:
return "tail"
print TC()
def ply(flips):
for i in range(flips):
return TC()
print ply(100)
When I run it it just says 'none.' Please tell me where I am going wrong. Thank You!
Just to start, your method naming is very bad. I doubt this is how your professor is teaching you to name methods and variables. It's ugly, against Python standards and hard to read I suggest you take some time and read PEP 8 it's how python was intended to be written.
So instead of TC you should use something like flip_coin and instead of ply use something like play_coin_flip or even simply play.
Next I don't know if I'm stepping outside of what you have learned but instead of using randon.randint you can use randon.choice.
And finally, as others have said, when you return you quit any other execution in a function and return whatever variable you retrun in that statement thus nullifying any other iterations of the loop you're performing. I suggest something like the below as a better program with corrections applied to make it function as intended.
from random import choice
faces = ['head', 'tail']
def flip_coin():
face = choice(faces)
return face
def play_coin_flip(flips = 1):
for i in range(flips):
print(flip_coin)
if __name__ == "__main__":
play_coin_flip(100)
*I'm a Beginner...
My friend tried to help me a bit with this but I can't seem to solve it. I'm not really sure what to do so any help would be greatly appreciated.I get the following error in averageMPG,"name stats city is parameter and global".I also wasn't really sure how to write both functions in my readData function as you can see. The problem is in the picture. I haven't succeeded in part b so I haven't moved on,
def readData(carmodelData_city):
global stats_city,stats_hwy
infile=open("carModelData_city", 'r')
stats_city=[]
for s in infile.read.split():
stats.append(float(s))
return stats_city
def read_Data(carmodelData_hwy):
global stats_city,stats_hwy
infile=open("carModelData_hwy", 'r')
stats_hwy=[]
for s in infile.read.split():
stats.append(float(s))
return stats_hwy
def averageMPG(stats_city, stats_hwy):
global stats_city,stats_hwy
totals=sum(stats_city)
length=len(stats_city)
avg1=totals/length
print("The averge mpg city is", avg1)
totals1=sum(stats_hwy)
length1=len(stats_hwy)
avg2=totals/length
print("The average mpg highway is", avg2)
average=(avg1+avg2)/2
print("The combined averge mpg is", average)
def main():
global stats_city,stats_hwy
stats_city=readData("carModelData_city", "r")
stats_hwy=read_Data("carModelData_hwy", "r")
[enter image description here][1]main()
You named a function parameter stats_city, and also declared it a global value. Those two things are incompatible.
AFAICT, none of your code actually requires anything to be global in the first place, so stop declaring everything global, and you should be fine.
Well, fine on that specific error anyway. The massive overuse of global here feels an awful lot like cargo cult programming, and you have many other problems (e.g. infile.read.split() is going to try to split the read method of the file; you forgot parens, so it's not actually calling read to get data back). You're also returning at the end of the first iteration of each loop, when I suspect you want to finish the loops and return the accumulated values. You need to learn a lot more of the basics here; please talk to a professor or a tutor.
Also, your "stats.append()" calls should probably be "stats_city.append" in the first function and "stats_hwy.append" in the second. You will return after one iteration in each function unless you adjust your idents on the return call.
I am teaching myself Python and am trying out a challenge I found to create a quote program for a gardener. I have almost all of it working and have added in iteration so that the user can make more than one quote without re-starting the program.
It produces the quote perfectly the first time but on the second run it presents this error:
Traceback (most recent call last):
File "/Users/shaunrogers/Desktop/Plymstock Prep/GCSE CS/SOL/Controlled Assessment/Sample Papers Solutions/gardening Task 2.py", line 105, in <module>
lawn = m2_items("lawn",0)
File "/Users/shaunrogers/Desktop/Plymstock Prep/GCSE CS/SOL/Controlled Assessment/Sample Papers Solutions/gardening Task 2.py", line 23, in m2_items
minutes = area*time[index]
TypeError: 'float' object is not subscriptable
I have the following code as a function that is producing the error:
def m2_items (item,index):
global costs, time, LABOUR
length = int(input("How long is the "+ item+"?\n"))
width = int(input("How wide is the "+item+"?\n"))
area = length*width
cost_m2 = float(costs[index])
total_cost = area*cost_m2
minutes = area*time[index]
hours = int(minutes/60)
labour = LABOUR*hours
labour_cost=round(labour,2)
m2_details = [area, cost_m2, total_cost,hours, labour_cost]
return m2_details
I have tried re-setting the local variables on the running of the function (but I didn't think this was needed as the variables should be removed from memory once the function has run).
I hope the question is clear and that I can get some insight. To re-iterate, what I want the program to do is allow me to call this function multiple times.
You are using the global time variable, which is initially subscriptable (probably an array). As your program continues, some other part of your code will assign a new value to time, maybe accidentally because you wrote time = some_calculation() instead of time[i] = some_calculation(), or maybe you are using the name time somewhere else without realizing it's already in use.
Do a search for all the places where you use the name time and you will probably find your error.
This is a common problem with global variables. Sometimes something updates them from another part of the code, and the error will sneak up on you like this.
I'm having a weird issue with numpy right now on a current assignment. I'm making an ant colony AI for a class (based on the Google AI Ants Challenge), and I'm using a diffusion based approach where I essentially diffuse out a scent from food/enemy hills on each turn. I've been using numpy since each turn basically consists of doing a lot of matrix manipulations, but I just recently got a weird bug that I can't figure out.
At the beginning of each turn, I update the field associated with each scent before I run the diffusion iterations:
# Here I update the "potential" field (hills_f) and the
# diffusion values (hills_l) for the hills scent. Diffusion values
# (lambda values) are 1 except for on ants, where they are higher
# or lower depending on their colony.
self.hills_f *= TURN_DECAY
self.hills_l = np.ones_like(self.hills_l)
# Update the lambda matrix
for r,c in ants.my_ants():
self.hills_l[r][c] = MY_HILLS_LAMBDA
for r,c in ants.enemy_ants():
self.hills_l[r][c] = ENEMY_HILLS_LAMBDA
So this code runs at the beginning of each turn (along with a similar snippet for the food scent), but on a random turn (ranges from 10-40), I get the following error:
Traceback (most recent call last):
File "long_file_path...", line 167, in run
bot.do_turn(ants)
File "MyBot.py", line 137, in do_turn
self.hills_l[r][c] = ENEMY_HILLS_LAMBDA
TypeError: 'numpy.float64' object does not support item assignment
It looks like it randomly turns self.hills_l into a scalar between the two for-loops, which doesn't make any sense to me. It's also weird that there's similar code for the food scent, which doesn't crash ever, and that this problem shows up so non-deterministically.
I can post more code if necessary, but I think everything should be there, especially since the problem seems to occur between the for loops.
Thanks!