If statement syntax error

[OkieWolf]

@ccc
Could you please explain how this works in more detail?
I realize you’ve renamed textfields but I’m not exactly understanding how the code is working. I’m mainly not understanding what’s happening with the or 0 and then the if len([x for x in (hypotenuse, short, long) if x]) != 2

hypotenuse = float(v['hypotenuse'].text or 0)
    short = float(v['short'].text or 0)
    long = float(v['long'].text or 0)
    if len([x for x in (hypotenuse, short, long) if x]) != 2: ```

[mcriley821]

@OkieWolf

hypotenuse = float(v['hypotenuse'].text or 0)
    short = float(v['short'].text or 0)
    long = float(v['long'].text or 0)
    if len([x for x in (hypotenuse, short, long) if x]) != 2: ```

v['short'].text or 0 will choose 0 if the text is "". You won’t hit an exception for a blank textfield. You will get an error if the text is alphabetical though.

(hypotenuse,short,long) is a tuple and [x for x in (hypotenuse,short,long) if x] is a list comprehension that steps through the tuple
and makes a list of the values that exist. Then if the length of that list isn’t 2, then you don’t have a correct input

[OkieWolf]

I need to probably rewrite the whole program because I’ve added more error trapping and a fourth textfield. It has increased complexity quite a bit, at least for me. It now cycles through all four textfields, find any two valid fields, decides whether to use Pythagorean Theorem or plain trig, and checks all for errors. One error in particular is that it is possible with the answers to have the short side of the triangle be longer than the long side. Obviously this can never happen so it’s now trapped and alerts the user.
Below is what I now have. I realize my code is a longer than it needs to be and fairly cumbersome at this point but I’m just learning Python and intend to try to rewrite it in a better and more efficient way.

def button3_tapped(sender):
	if (v['textfield3'].text)!="" and (v['textfield4'].text)!="":
		v['label7'].background_color = 'white'
		v['label7'].text_color = 'white'
		v['label7'].text = ''
		hyp = float(v['textfield3'].text)
		sht = float(v['textfield4'].text)
		hypa = hyp
		shta = sht
		hyp = pow(hyp,2)
		sht = pow(sht,2)
		lng = math.sqrt(hyp - sht)
		lnga = lng
		ang = math.asin(shta/hypa)
		ang = math.degrees(ang)
		v['textfield5'].text_color = 'green'
		v['textfield5'].text = str(lng)
		v['textfield6'].text_color = 'green'
		v['textfield6'].text = str(ang)
		shtb = float(v['textfield4'].text)
		lngb = float(v['textfield5'].text)
		if shtb > lngb:
			v['label7'].background_color = 'red'
			v['label7'].text_color = 'white'
			v['label7'].text = 'ERROR. Short side cannot be longer than long side.'
	elif (v['textfield4'].text)!="" and (v['textfield5'].text)!="":
		v['label7'].background_color = 'white'
		v['label7'].text_color = 'white'
		v['label7'].text = ''
		sht = float(v['textfield4'].text)
		shta = sht
		lng = float(v['textfield5'].text)
		lnga = lng
		sht = pow(sht,2)
		lng = pow(lng,2)
		hyp = math.sqrt(sht + lng)
		hypa = hyp
		ang = math.asin(shta/hypa)
		ang = math.degrees(ang)
		v['textfield3'].text_color = 'green'
		v['textfield3'].text = str(hyp)
		v['textfield6'].text_color = 'green'
		v['textfield6'].text = str(ang)
		shtb = float(v['textfield4'].text)
		lngb = float(v['textfield5'].text)
		if shtb > lngb:
			v['label7'].background_color = 'red'
			v['label7'].text_color = 'white'
			v['label7'].text = 'ERROR. Short side cannot be longer than long side.'
	elif (v['textfield3'].text)!="" and (v['textfield5'].text)!="":
		v['label7'].background_color = 'white'
		v['label7'].text_color = 'white'
		v['label7'].text = ''
		hyp = float(v['textfield3'].text)
		hypa = hyp
		lng = float(v['textfield5'].text)
		lnga = lng
		hyp = pow(hyp,2)
		lng = pow(lng,2)
		sht = math.sqrt(hyp - lng)
		shta = sht
		ang = math.asin(shta/hypa)
		ang = math.degrees(ang)
		v['textfield4'].text_color = 'green'
		v['textfield4'].text = str(sht)
		v['textfield6'].text_color = 'green'
		v['textfield6'].text = str(ang)
		shtb = float(v['textfield4'].text)
		lngb = float(v['textfield5'].text)
		if shtb > lngb:
			v['label7'].background_color = 'red'
			v['label7'].text_color = 'white'
			v['label7'].text = 'ERROR. Short side cannot be longer than long side.'
	elif (v['textfield3'].text)!="" and (v['textfield6'].text)!="":
		v['label7'].background_color = 'white'
		v['label7'].text_color = 'white'
		v['label7'].text = ''
		hyp = float(v['textfield3'].text)
		ang = float(v['textfield6'].text)
		ang = math.radians(ang)
		hypa = hyp
		sht = hyp * math.sin(ang)
		shta = sht
		hypc = pow(hyp,2)
		shtc = pow(sht,2)
		lng = math.sqrt(hypc - shtc)
		lnga = lng
		v['textfield5'].text_color = 'green'
		v['textfield5'].text = str(lng)
		v['textfield4'].text_color = 'green'
		v['textfield4'].text = str(sht)
		shtb = float(v['textfield4'].text)
		lngb = float(v['textfield5'].text)
		if shtb > lngb:
			v['label7'].background_color = 'red'
			v['label7'].text_color = 'white'
			v['label7'].text = 'ERROR. Short side cannot be longer than long side.'
	elif (v['textfield4'].text)!="" and (v['textfield6'].text)!="":
		v['label7'].background_color = 'white'
		v['label7'].text_color = 'white'
		v['label7'].text = ''
		sht = float(v['textfield4'].text)
		ang = float(v['textfield6'].text)
		ang = math.radians(ang)
		shta = sht
		hyp = sht / math.sin(ang)
		hypa = hyp
		hypc = pow(hyp,2)
		shtc = pow(sht,2)
		lng = math.sqrt(hypc - shtc)
		shta = sht
		v['textfield5'].text_color = 'green'
		v['textfield5'].text = str(lng)
		v['textfield3'].text_color = 'green'
		v['textfield3'].text = str(hyp)
		shtb = float(v['textfield4'].text)
		lngb = float(v['textfield5'].text)
		if shtb > lngb:
			v['label7'].background_color = 'red'
			v['label7'].text_color = 'white'
			v['label7'].text = 'ERROR. Short side cannot be longer than long side.'
	elif (v['textfield5'].text)!="" and (v['textfield6'].text)!="":
		v['label7'].background_color = 'white'
		v['label7'].text_color = 'white'
		v['label7'].text = ''
		lng = float(v['textfield5'].text)
		ang = float(v['textfield6'].text)
		ang = math.radians(ang)
		lnga = lng
		hyp = lng / math.cos(ang)
		hypa = hyp
		hypc = pow(hyp,2)
		lngc = pow(lng,2)
		sht = math.sqrt(hypc - lngc)
		shta = sht
		v['textfield4'].text_color = 'green'
		v['textfield4'].text = str(sht)
		v['textfield3'].text_color = 'green'
		v['textfield3'].text = str(hyp)
		shtb = float(v['textfield4'].text)
		lngb = float(v['textfield5'].text)
		if shtb > lngb:
			v['label7'].background_color = 'red'
			v['label7'].text_color = 'white'
			v['label7'].text = 'ERROR. Short side cannot be longer than long side.'
	else:
		v['label7'].background_color = 'red'
		v['label7'].text_color = 'white'
		v['label7'].text = 'ERROR' ```

[OkieWolf]

If you import math why do you still have to say math.sqrt and math.cos?
But then other things like pow don’t have to say math.pow.

[ccc]

pow() is a Python builtin. https://docs.python.org/3/library/functions.html

You can also say from math import cos, sin, tan to use the single word functions.

[OkieWolf]

This post is deleted!

[OkieWolf]

@ccc

I’m attempting to rewrite my code to be more efficient and am utilizing a couple of code snippets that a couple of you have supplied. However, in the below code I noticed that the output is 0.0 if both inputs happen to be the same number. I’m not understanding why.

def button3_tapped(sender):
	hypotenuse = float(v['hypotenuse'].text or 0)
	short = float(v['short'].text or 0)
	long = float(v['long'].text or 0)
	if len([x for x in (hypotenuse, short, long) if x]) != 2:
		v['mess'].text = "Enter two fields"
		v['mess'].background_color = 'red'
		v['mess'].text_color = 'white'
		return
	if hypotenuse:
		if short and not long:
			v['long'].text = str(math.sqrt(hypotenuse ** 2 - short ** 2))
			v['long'].text_color = 'green'
		elif long and not short:
			v['short'].text = str(math.sqrt(hypotenuse ** 2 - long ** 2))
			v['short'].text_color = 'green'
	else:
		v['hypotenuse'].text = str(math.sqrt(short ** 2 + long ** 2))
		v['hypotenuse'].text_color = 'green' ```

[ccc]

if both inputs happen to be the same number

if hypotenuse:
    if short:
        The rules of math say that the hypotenuse must be greater than short.
    else
        The rules of math say that the hypotenuse must be greater than long.
else:
    short could be the same number as long  # <-- this is the only instance where both inputs could be the same number

if hypotenuse and (short >= hypotenuse or long >= hypotenuse):
    raise ValueError("Not allowed by the rules of math.")

[OkieWolf]

Agreed. It works fine if short and long are the same number, which equals 45 degrees.

[OkieWolf]

Here’s what I came up with. It’s much shorter and easier to understand and I GREATLY appreciate all the help and patience.
This version does all the other one did plus more. This version will calculate the other side and angle based on two sides input and can now calculate any side of the triangle based on angle and any one of the three sides.

def button3_tapped(sender):
	hypotenuse = float(v['hypotenuse'].text or 0)
	short = float(v['short'].text or 0)
	long = float(v['long'].text or 0)
	angle = float(v['angle'].text or 0)
	if len([x for x in (hypotenuse, short, long, angle) if x]) != 2:
		v['mess'].text = "Enter two fields"
		v['mess'].background_color = 'red'
		v['mess'].text_color = 'white'
		return
	if hypotenuse and not angle:
		if short and not long:
			v['long'].text = str(math.sqrt(hypotenuse ** 2 - short ** 2))
			v['long'].text_color = 'green'
			v['angle'].text = str(math.degrees(math.asin(short / hypotenuse)))
			v['angle'].text_color = 'green'
		elif long and not short:
			v['short'].text = str(math.sqrt(hypotenuse ** 2 - long ** 2))
			v['short'].text_color = 'green'
			v['angle'].text = str(math.degrees(math.acos(long / hypotenuse)))
			v['angle'].text_color = 'green'
	else:
		if not angle:
			v['hypotenuse'].text = str(math.sqrt(short ** 2 + long ** 2))
			v['hypotenuse'].text_color = 'green'
			v['angle'].text = str(math.degrees(math.atan(short / long)))
			v['angle'].text_color = 'green'
		
	if angle:
		angle = math.radians(angle)
		if short and not long and not hypotenuse:
			v['hypotenuse'].text = str(short / (math.sin(angle)))
			v['hypotenuse'].text_color = 'green'
			v['long'].text = str(short / (math.tan(angle)))
			v['long'].text_color = 'green'
		elif long and not short and not hypotenuse:
			v['hypotenuse'].text = str(long / (math.cos(angle)))
			v['hypotenuse'].text_color = 'green'
			v['short'].text = str(long * (math.tan(angle)))
			v['short'].text_color = 'green'
		elif angle and hypotenuse and not long and not short:
			v['short'].text = str(hypotenuse * (math.sin(angle)))
			v['short'].text_color = 'green'
			v['long'].text = str(hypotenuse * (math.cos(angle)))
			v['long'].text_color = 'green' 

[ccc]

Please put the trailing three backticks on a line all by themselves.

[OkieWolf]

@ccc
Done

[ccc]

OK. Now it is time to separate the business logic from the UI representation. We would need to put all the math logic in a function of the form:

def triangle(a, b, hypotenuse=0, angle=45):
    pass  # math logic goes here

Where triangle(3, 4) returns (3, 4, 5.0, 45)
Where triangle(3, 0) would raise ValueError()

[JonB]

It seems to me you could also dispense with most of the long / short specific logic, and just compute the other edge, then figure out which one is the long vs short after the fact.

[OkieWolf]

@ccc

Please explain

def triangle(a, b, hypotenuse=0, angle=45):
    pass  # math logic goes here
Where triangle(3, 4) returns (3, 4, 5.0, 45)
Where triangle(3, 0) would raise ValueError() 

[ccc]

This was an invitation for you or someone else to write a function that can take between 2 and 4 parameters and calculate all other variables or raise an exception if there is no possible solution. This function would allow us to isolate all UI operations from all math operations. It would make it easier to test our math operations without the UI and would allow us to easily port the math operations to a different platform.

[OkieWolf]

@ccc

Below will calculate short and long with given hypotenuse and angle but you have to enter zero for short and long input.

import math

def triangle(short, long, hypotenuse, angle):
    pass  
    if hypotenuse and angle:
    	angle = math.radians(angle)
    	print ('Short = ' + str(hypotenuse * (math.sin(angle))))
    	print ('Long = ' + str(hypotenuse * (math.cos(angle))))
    	
triangle(0,0,10,30)

[OkieWolf]

@ccc

This will calculate any side or angle. But input still has to be zero for unknowns at input.

import math

def triangle(short, long, hypotenuse, angle):
    pass
    if len([x for x in (hypotenuse, short, long, angle) if x]) == 2:
    	if hypotenuse and angle:
    		angle = math.radians(angle)
    		print	('Short = ' + str(hypotenuse * (math.sin(angle))))
    		print	('Long = ' + str(hypotenuse * (math.cos(angle))))
    	elif long and angle:
    		angle = math.radians(angle)
    		print	('Short = ' + str(long * (math.tan(angle))))
    		print	('Hypotnuse = ' + str(long / (math.cos(angle))))
    	elif short and angle:
    		angle = math.radians(angle)
    		print	('Long = ' + str(short / (math.tan(angle))))
    		print	('Hypotnuse = ' + str(short / (math.sin(angle))))
    	elif hypotenuse and short:
    		print ('Long = ' + str(math.sqrt(hypotenuse ** 2 - short ** 2)))
    		print ('Angle = ' + str(math.degrees(math.asin(short / hypotenuse))))
    	elif hypotenuse and long:
    		print ('Short = ' + str(math.sqrt(hypotenuse ** 2 - long ** 2)))
    		print ('Angle = ' + str(math.degrees(math.acos(long / hypotenuse))))
    	elif short and long:
    		print ('Hypotenuse = ' + str(math.sqrt(short ** 2 + long ** 2)))
    		print ('Angle = ' + str(math.degrees(math.atan(short / long))))
    else:
    	print ("ERROR")

triangle(5,0,10,0) 

[ccc]

Step 0: drop the pass line.
Step 1:

    if len([x for x in (hypotenuse, short, long, angle) if x]) != 2:
        raise ValueError("Exactly two parameters must be zero.")

Step 2: change triangle() so it never prints but instead returns the answer with the statement return short, long, hypotenuse, angle
Step 3: change triangle(5,0,10,0) to print(triangle(5,0,10,0)).

Step 1: is called a fast-fail which is safer and more readable than failing later in the function. Basically is says "I see a bad situation (bad input data) so I am going to raise an exception and stop processing".

[mikael]

@ccc, I am sure I just saw you using count somewhere:

if (hyp, ...).count(0) != 2:
    raise ...