Develop Reference

Python Linking Variable Values

I want to to store a reference to a class object inside a dictionary or another class that will maintain the same value as the actual class object. Currently, I'm using a string of the class object and the eval() function. I know this isn't a proper solution but haven't found another fix.
curWeapon is a object of WeaponInfo with pveFlag and pvpFlag variables
ListSetting stores the boolean expression of curWeapon along with a,b,c...
wishLists is passed to the main class of the program which reads a file and changed the pve/pvpFlags
When a empty line is read the boolean expression is evaluated with the new flags
wishLists.append(ListSetting("curWeapon.pveFlag or not curWeapon.pvpFlag", a, b, c, d))
My only idea is making a new function that has separates the boolean expression from a,b,c.. when making the ListSetting and adding that separately. Although I'm not sure if wishLists would update the firstFlag, secondFlag... variables.
firstFlag = ListSetting(a,b,c,d)
wishLists.append(firstFlag)
def wishListFlags():
firstFlag.flags = curWeapon.pveFlag or not curWeapon.pvpFlag
secondFlag.flags = ""
...
I'm pretty sure that updating the index of wishLists would work but would need a bunch of if statements or a dictionary.
firstFlag = ListSetting(a,b,c,d)
wishLists.append(firstFlag)
flagExpressions = {
1 : curWishListcurWeapon.pveFlag or not curWeapon.pvpFlag,
2 : "",
...}
def wishListFlags():
for index in len(wishLists):
wishLists[index].flags = flagExpressions.get(index)
If anyone knows a better way to go about this please let me know. Also, if my examples aren't specific enough or are confusing I'd be happy to share my entire program, I didn't know if it would be too much.

To store an expression you use a function, which you later call to get the value of the expression.
flagExpressions = {
1: lambda: curWishListcurWeapon.pveFlag or not curWeapon.pvpFlag
2: lambda: ""
}
def wishListFlags():
for index in len(wishLists):
wishLists[index].flags = flagExpressions.get(index, lambda: None)()

Call many python functions from a module by looping through a list of function names and making them variables

I have three similar functions in tld_list.py. I am working out of mainBase.py file.
I am trying to create a variable string which will call the appropriate function by looping through the list of all functions. My code reads from a list of function names, iterates through the list and running the function on each iteration. Each function returns 10 pieces of information from separate websites
I have tried 2 variations annotated as Option A and Option B below
# This is mainBase.py
import tld_list # I use this in conjunction with Option A
from tld_list import * # I use this with Option B
functionList = ["functionA", "functionB", "functionC"]
tldIterator = 0
while tldIterator < len(functionList):
# This will determine which function is called first
# In the first case, the function is functionA
currentFunction = str(functionList[tldIterator])
Option A
currentFunction = "tld_list." + currentFunction
websiteName = currentFunction(x, y)
print(websiteName[1]
print(websiteName[2]
...
print(websiteName[10]
Option B
websiteName = currentFunction(x, y)
print(websiteName[1]
print(websiteName[2]
...
print(websiteName[10]
Even though it is not seen, I continue to loop through the iteration by ending each loop with tldIterator += 1
Both options fail for the same reason stating TypeError: 'str' object is not callable
I am wondering what I am doing wrong, or if it is even possible to call a function in a loop with a variable

You have the function names but what you really want are the function objects bound to those names in tld_list. Since function names are attributes of the module, getattr does the job. Also, it seems like list iteration rather than keeping track of your own tldIterator index would suffice.
import tld_list
function_names = ["functionA", "functionB", "functionC"]
functions = [getattr(tld_list, name) for name in function_names]
for fctn in functions:
website_name = fctn(x,y)

You can create a dictionary to provide a name to function conversion:
def funcA(...): pass
def funcB(...): pass
def funcC(...): pass
func_find = {"Huey": funcA, "Dewey": funcB, "Louie": FuncC}
Then you can call them, e.g.
result = func_find["Huey"](...)

You should avoid this type of code. Try using if's, or references instead. But you can try:
websiteName = exec('{}(x, y)'.format(currentFunction))

Small python program involving newton method

I'm trying to write a small program in python that involves(among other things) Newton method, but i'm encountering several problems, that are probably pretty basic, but since I'm new at programming, i cant overcome..
First i defined the function and it's derivative:
import math
def f(x,e,m):
return x-e*math.sin(x)-m
def df(x,e):
return 1-e*math.cos(x)
def newtons_method(E0,m,e,q):#q is the error
while abs(f(E0,e,m))>q:
E=E0-f(E0,e,m)/df(E0,e)
E0=E
return (E0)
def trueanomaly(e,E):
ta=2*math.arctan(math.sqrt((1+e)/(1-e))*math.tan(E))
return (ta)
def keplerianfunction(T,P,e,K,y,w):
for t in frange (0,100,0.5):
m=(2*math.pi*((t-T)/P))
E0=m+e*math.sin(m)+((e**2)/2)*math.sin(2*m)
newtons_method(E0,m,e,0.001)
trueanomaly(e,E0)
rv=y+K*(e*math.cos(w)+math.cos(w+ta))
return (ta)","(rv)
def frange(start, stop, step):
i = start
while i < stop:
yield i
i += step
The question is that this keeps giving me errors, indentation errors and stuff, especially in the keplerianfunction ... Can someone help me? what am I doing wrong here?
Thank you in advance!

Many things are wrong with this code, and I don't know what the desired behaviour is so can't guarantee that this will help, but I'm going to try and help you debug (although it looks like you mostly need to re-read your Python coursebook...).
First, in most languages if not all, there is a thing called the scope: a variable, function, or any other object, exists only within a certain scope. In particular, variables exist only in the scope of the function that they are defined in. This means that, to use the result of a function, you first need to return that result (which you are doing), and when you call that function you need to store that result into a variable, for example ta = trueanomaly(e, E0).
Then, you don't really need to use brackets when returning values, even if you want to return multiple values. If you do want to return multiple values though, you just need to separate them with a comma, but not with a string character of a comma: write return ta, rv instead of return ta","rv.
Finally, you seem to be iterating over a range of values, yet you don't return the whole range of values but either the first value (if your return is in the for loop), or the last one (if your return is under the for loop). Instead, you may want to store all the ta and rv values into one/two lists, and return that/those lists in the end, for example:
def keplerianfunction(T,P,e,K,y,w):
# Initialise two empty lists
tas = []
rvs = []
for t in frange (0,100,0.5):
m = 2*math.pi*((t-T)/P)
E0 = m+e*math.sin(m)+((e**2)/2)*math.sin(2*m)
E0 = newtons_method(E0,m,e,0.001)
ta = trueanomaly(e,E0)
rv = y+K*(e*math.cos(w)+math.cos(w+ta))
# At each step save the value for ta and rv into the appropriate list
tas.append(ta)
rvs.append(rv)
# And finally return the lists
return (tas,rvs)
Also, why using a new frange function when range has the exact same behaviour and is probably more efficient?

code runs else statement repeatedly

every time the below code runs, it goes straight through to the first else statement, then runs the next else statement four times. what is going on and how do I fix it so it calls the movement() module?
class square(object):
def __init__(self,updown,leftright,residence,name):
self.updown = updown
self.leftright = leftright
self.residence = bool
self.name = name
a1 = square(1,1,True,"a1")
a2 = square(2,1,False,"a2")
b1 = square(1,2,False,"b1")
b2 = square(2,2,False,"b2")
square_dict = {a1:"a1",a2:"a2",b1:"b1",b2:"b2"}
movement_select()
def movement_select():
response = raw_input("where would you like to move?")
if response in square_dict:
moveTo = square_dict[response]
else:
print "this runs once"
for a in square_dict:
if a.residence == True:
moveFrom = a
movement(moveFrom,moveTo)
else:
print "this runs four times"
movement_select()

Look at how you're defining residence:
self.residence = bool
So, for any square a, a.residence will be the type bool, never the boolean value True (or anything else). So this test will always fail:
if a.residence == True:
To fix it, change that first line to:
self.residence = residence
While we're at it, you rarely need == True, so you can also change the second line to:
if a.residence:
But that isn't a necessary fix, just a way of simplifying your code a bit.
Meanwhile, your squares_dict is a bit odd. I'm not sure whether it's incorrect or not, but let's take a look:
It maps from square objects to their names. That could be a useful thing to do. It means you can iterate over the dict and get all the squares—as you correctly do in your code. And if you later had a square and wanted to get its name, you could use square_dict for that. Then again, you could probably get the same benefit with just a square_list, and using the name already available as an attribute of the square objects (unless you need the same square to have different names in different contexts).
And meanwhile, a mapping in this direction can't be used for looking up squares_dict[response], because response is a name, not a square. So, you definitely need a mapping in the opposite direction, either in addition to or instead of this one.
If you scrap the square-to-name mapping and only keep the name-to-square mapping, you can still iterate over the squares; you'd just have to do for square in squares_dict.values(): instead of just for square in squares_dict:.

First problem: your dictionary appears to be backwards: you want to look up the square objects from their locations, rather than the other way around. This is why your first conditional is never true. You also might as well strip() the response to ensure that you don't have any hidden whitespace in there.
square_dict = {"a1":a1, "a2":a2, "b1":b1, "b2":b2}
# Later...
response = raw_input("where would you like to move?").strip()
# Later still...
for a in square_dict.values(): # Because we switched the dictionary around!
If you don't want to silently strip off the whitespace, I'd suggest that you at least echo their input back to them (print('"{}"'.format(response))) in the case that it's not found in your dictionary, so they (you) can be sure that at least the input was correct.
The second problem is because of how you define residence. You set the variable equal to bool, which is not what you want at all. Line five ought to read:
self.residence = residence
Finally, some other thoughts on your code! You check whether a value is True by checking if a.residence == True:. The preferred form of this comparison is the simpler version:
if a.residence:
Your methods could also be named more descriptively. Generally speaking, it's always nice to begin a function or method name with a verb, to improve readability. This is of course a question of style, but for instance, the two functions we see, movement_select and movement aren't extremely clear as to their function. It would be much easier to read if they used a standardized form, e.g. choose_move and perform_move.

self.residence = bool
should be
self.residence = residence

You don´t set residence right, this is wrong:
class square(object):
def __init__(self,updown,leftright,residence,name):
self.updown = updown
self.leftright = leftright
self.residence = bool
self.name = name
it has to be
class square(object):
def __init__(self,updown,leftright,residence,name):
self.updown = updown
self.leftright = leftright
self.residence = residence # not bool!!
self.name = name

Your response contains \n symbol, just strip() it
You should also swap places between keys and values in your dictionary

Python Newbie: Returning Multiple Int/String Results in Python

I have a function that has several outputs, all of which "native", i.e. integers and strings. For example, let's say I have a function that analyzes a string, and finds both the number of words and the average length of a word.
In C/C++ I would use # to pass 2 parameters to the function. In Python I'm not sure what's the right solution, because integers and strings are not passed by reference but by value (at least this is what I understand from trial-and-error), so the following code won't work:
def analyze(string, number_of_words, average_length):
... do some analysis ...
number_of_words = ...
average_length = ...
If i do the above, the values outside the scope of the function don't change. What I currently do is use a dictionary like so:
def analyze(string, result):
... do some analysis ...
result['number_of_words'] = ...
result['average_length'] = ...
And I use the function like this:
s = "hello goodbye"
result = {}
analyze(s, result)
However, that does not feel right. What's the correct Pythonian way to achieve this? Please note I'm referring only to cases where the function returns 2-3 results, not tens of results. Also, I'm a complete newbie to Python, so I know I may be missing something trivial here...
Thanks

python has a return statement, which allows you to do the follwing:
def func(input):
# do calculation on input
return result
s = "hello goodbye"
res = func(s) # res now a result dictionary
but you don't need to have result at all, you can return a few values like so:
def func(input):
# do work
return length, something_else # one might be an integer another string, etc.
s = "hello goodbye"
length, something = func(s)

If you return the variables in your function like this:
def analyze(s, num_words, avg_length):
# do something
return s, num_words, avg_length
Then you can call it like this to update the parameters that were passed:
s, num_words, avg_length = analyze(s, num_words, avg_length)
But, for your example function, this would be better:
def analyze(s):
# do something
return num_words, avg_length

In python you don't modify parameters in the C/C++ way (passing them by reference or through a pointer and doing modifications in situ).There are some reasons such as that the string objects are inmutable in python. The right thing to do is to return the modified parameters in a tuple (as SilentGhost suggested) and rebind the variables to the new values.

If you need to use method arguments in both directions, you can encapsulate the arguments to the class and pass object to the method and let the method use its properties.