here is some code. I want to make an if statement but only when a variable has increased
while True:
a += 1
if a ????
print('a has changed')
Here is an option.
while True:
previous = a
# do stuff
a += 1
if a != previous:
print('a has changed')
Here is a way you can do this:
while True:
old_a = a #Create a variable for the old value of a
a += 1
if a > old_a: #Check the condition if value of a has increased.
print('a has changed')
A more clever way using the python Observer pattern.
class observe_value_change():
def __init__(self):
self._initial = 1
#property
def position(self):
return self._initial
#position.setter
def position(self, new_value):
self._initial = new_value
print("execute more code here!")
print(self._initial)
To test
p = observe_value_change()
print(p.position)
p.position = 4
Explanation:
When the value of position changes, it will call the position setter method otherwise it will not be called.
So, the if block can be written inside the position setter method.
Related
I need to overload the addition function so that it takes in the first point and the end point as the left and right side of the equation and outputs the equation. This is what my code looks right now. I'm not sure how to involve the line class?
import math
class Point:
'''Class that creates points. Attributes: Eastings and Northings'''
def __init__(self,x,y):
self.eastings = x
self.northings = y
def getCoords(self):
self.coords = (self.eastings,self.northings)
return self.coords
def setCoords(self,other_x,other_y):
self.eastings = float(other_x)
self.northings = float(other_y)
def __str__(self):
return f"{self.eastings},{self.northings}"
def __add__(self,new_point):
pass
#creates a line (new class)
class Line(Point):
'''Class that creates line object based on two points'''
def __init__(self,start,end):
self.start = start #Type:Point (x1,y1)
self.end = end #Type:Point (x2,y2)
self.latitude = abs(self.end.eastings - self.start.eastings)
self.departure = abs(self.end.northings - self.start.northings)
self.distance = math.sqrt((self.latitude)**2 + (self.departure)**2)
self.azimuth = math.degrees(math.atan2(self.departure,self.latitude))
def __getitem__(self,key):
if key == 0:
ans = self.start
elif key == 1:
ans = self.end
else:
print("invalid index")
return ans
#test code
a = Point(0,0)
b = Point(1,1)
c = Point(1,0.5)
line1 = a+b
print((type(line1))
The test code is supposed to print out the type as class line.
There's nothing that says the __add__() method has to return a the same type as the instance — which means you could this:
class Point:
...
def __add__(self, other):
if isinstance(other, Point):
return Line(self, other) # Line from this Point to the other.
else:
raise TypeError(f"Can't add a non-Point to a Point}")
Be careful doing this however, because the Line class will inherit the method (so you probably need to modify its version of it).
Add a self.getCoords() call to your Point.__init__() method.
Add return Line(self, new_point) to your Point.__add__() method.
Testing:
a = Point(0,0)
b = Point(1,1)
c = Point(1,0.5)
line1 = a+b
print(type(line1)) # I have removed a round bracket on the left
Output: <class '__main__.Line'>
In case you want to run a block of code, where a function/method has not one line in it, you have to add a pass to it. Otherwise you will get an error, because the structure requires it. Or you comment the function declaration out.
Consider this piece of code, wondering would it be possible to return a value before it gets updated.
class A:
def __init__(self):
self.n = 0
def get_next(self):
return self.n++ # Return its current value. after it gets returned, update n.
a = A()
a.get_next() # return 0
a.get_next() # return 1
This'll work:
def get_next(self):
old_value = self.n
self.n += 1
return old_value
Learning python from Udacity. Exercise is mentioned below. I cannot see where output 'None' is coming from. Is there something about classes that I am missing ? Thx in advance
Output is always
0
None
======= CODE BEGIN ==============
"""You can use this class to represent how classy someone
or something is.
"Classy" is interchangable with "fancy".
If you add fancy-looking items, you will increase
your "classiness".
Create a function in "Classy" that takes a string as
input and adds it to the "items" list.
Another method should calculate the "classiness"
value based on the items.
The following items have classiness points associated
with them:
"tophat" = 2
"bowtie" = 4
"monocle" = 5
Everything else has 0 points.
Use the test cases below to guide you!"""
class Classy(object):
def __init__(self):
self.items = []
self.classiness = 0
def getClassiness(self):
print(self.classiness)
def createList(self):
self.items.append(item)
def addItem(self, item):
if item=="tophat":
self.classiness+=2
elif item=="bowtie":
self.classiness+=4
elif item=="monocle":
self.classiness+=5
else:
self.classiness+=0
return self.classiness
# Test cases
me = Classy()
# Should be 0
print(me.getClassiness())
Your method getClassiness() is printing and the caller is also printing.
Maybe you meant to return a value rather than printing?
def getClassiness(self):
return self.classiness
class Classy(object):
def __init__(self):
self.items = []
self.classiness = 0
def getClassiness(self):
return self.classiness
def createList(self):
self.items.append(item)
def addItem(self, item):
if item=="tophat":
self.classiness+=2
elif item=="bowtie":
self.classiness+=4
elif item=="monocle":
self.classiness+=5
else:
self.classiness=0
Test cases
me = Classy()
Should be 0
print(me.getClassiness())
I have a class for a Dialogue system as follows
class DIALOGUE(object):
def __init__(self, place, who, sTime, eTime, isActive, mood, menuText, func, repeatable, num):
self.place = place
self.who = who
self.sTime = sTime
self.eTime = eTime
self.isActive = isActive
self.mood = mood
self.menuText = menuText
self.func = func
self.repeatable = repeatable
self.num = num
#property
def ACheck(self):
global Date
if self.sTime == "none":
return True
else:
tHour,tMin = self.sTime.split(":")
if tHour >= Date.Hour and tMin <= Date.Minute:
tHour,tMin = self.eTime.split(":")
if tHour < Date.Hour and tMin < Date.Minute:
return True
return False
#property
def BCheck(self):
global Act
if self.who == Act:
return True
else:
return False
#property
def CCheck(self):
global Location
if self.place == Location:
return True
if self.place == "none":
return True
return False
#property
def DCheck(self):
if self.repeatable:
return True
else:
if self.num > 0:
return False
else:
return True
#property
def CanChat(self):
if self.isActive and self.ACheck and self.BCheck and self.CCheck and self.DCheck:
return True
else:
return False
def SetActive(self):
self.isActive = True
def Do(self):
self.num += 1
renpy.call(self.func)
Most of this should be self explanatory but I parse an XML file into a list of Instances of this class.
The user is presented with a list of available dialogues based on what Location they are in, what time of day it is and what NPC they have selected. If the dialogue is not repeatable The DCheck method looks at whether or not the dialogue has been completed before i.e if the dialogue is not repeatable and self.num > 0 the method will return False
Essentially it loops through all the dialogues and carries out i.CanChat and if this value returns True, the Dialogue is added to the menu
The issue I'm having is that the Check methods aren't returning the correct value. Specifically DCheck is returning True all the time, regardless of whether the Dialogue is repeatable or not, and ignoring the value of self.num
The class is created in an init python: block and then the xml file is parsed in a separate python block which is called from inside the start label
It's probably something really simple but I can't figure it out.
The list of instances is parsed as follows
Dialogues = []
for j in Dialo:
JPlace = j.find('Place').text
JWho = j.find('Who').text
JsTime = j.find('Start').text
JeTime = j.find('End').text
JMood = int(j.find('Mood').text)
JText = j.find('Text').text
JFunc = j.find('Func').text
JRep = j.find('Rep').text
if JRep == "True":
Jrep = True
else:
Jrep = False
Dialogues.append(DIALOGUE(JPlace, JWho, JsTime, JeTime, False, JMood, JText, JFunc, JRep, 0))
The method for creating the menu is as follows
def TalkCheck():
talks = []
talks.append(("Nevermind.", "none"))
for i, q in enumerate(Dialogues):
if q.CanChat:
talks.append((q.menuText,i))
renpy.say(None, "", interact=False)
talkchoice = renpy.display_menu(talks)
if talkchoice <> "none":
talkchoice = int(talkchoice)
Dialogues[talkchoice].Do()
Your question is incomplete - you didn't post a MCVE, we don't know the effective values for "repeatble" and "num" that leads to this behaviour, and we don't even know if it's using Python 2.x or Python 3.x - so we can just try and guess. Now since you mention that you "parse an XML file into a list of instances", I stronly suspect you are running Python 2.x and passing those values as strings instead of (resp.) boolean and int. In Python 2, "-1" (string) compares greater than 0 (int) - it raises a TypeError in Python 3.x -, and in both cases a non-empty string evals to True in a boolean context (bool('False') == True). Since there's no obvious logical error in your method implementation, that's the only explanation I can think of.
BTW, expressions have a boolean values and return exits the function, so you can simplify your code:
#property
def DCheck(self):
if self.repeatable:
return True
return self.num > 0
I'm trying to implement a recursive method to calculate the height of a binary tree. Here is the "height"-code:
def HeightOfTree(self):
if self.root is None:
return 0
else:
ans=self._HeightOfTree(self.root)
return ans
def _HeightOfTree(self,currentNode):
if currentNode.hasleftChild():
lheight=1+self._HeightOfTree(currentNode.leftChild)
if currentNode.hasrightChild():
rheight=1+self._HeightOfTree(currentNode.rightChild)
if lheight > rheight:
return (lheight+1)
else:
return (rheight+1)
When I try to call the function, I get the following error msg:
UnboundLocalError: local variable 'lheight' referenced before assignment
How can I fix this problem ?
If you're setting the value of a variable in an if block and you try to use it later, make sure that it's declared before the block so that if the if doesn't happen, it still exists.
Wrong:
if False:
x = 3
print(x)
# UnboundLocalError
Right:
x = 0
if False:
x = 3
print(x)
# 0
You are getting the UnboundLocalError because the values rheight and lheight are not created in the case that leftChild or rightChild are None.
It would be simpler if you defined a base case of _HeightOfTree(None) == 0:
def _HeightOfTree(self,currentNode):
if currentNode is None:
return 0
return 1 + max(self._HeightOfTree(currentNode.leftChild), self._HeightOfTree(currentNode.rightChild))