Length of a path in a 2-tuple.

[PythonNerd]

Some homework that I have been struggling on mainly because I am unsure how to proceed. I have all the formulas I need but I haven't been able to find a useful online tutorial for how to get the necessary information out of a 2-tuple.

print (pathLength2d ([(0,0), (1,1)])) 

import math

def length (v):

    """ Length of a vector in 2-space.

    Params: v (2-tuple) vector in 2-space
    Returns: (float) length
    """
    number = 0
    for i in range(len(str(v))):
        number += v[i]**2
    return math.sqrt(number)

I know that's an error as it's trying to multiply an index of (0,0) by itself. I'm not asking for a full out solution, but a pointer in the right direction.

Thanks!

[micseydel]

Could you provide a runnable snippet, and the full traceback that it produces? You first line of code calls a function you haven't defined, and I'm not sure what you're passing to length() or the exception you're having.

[ichabod801]

You can iterate directly over the tuple. Try:

for x in (1, 2):
    print(x)

If you know list comprehensions, you can use the sum function on one, and turn your function into one line of code. Otherwise you can drastically simplify your loop.

[PythonNerd]

Could you provide a runnable snippet, and the full traceback that it produces? You first line of code calls a function you haven't defined, and I'm not sure what you're passing to length() or the exception you're having.

My bad. Basically we have to cut the program up into sections. I finally got it to output but I cannot:
1) Find a use for the length function
2) Am off by a slight margin, probably some float issue

import math
def length (v):

    """ Length of a vector in 2-space.

    Params: v (2-tuple) vector in 2-space
    Returns: (float) length
    """
    return math.sqrt(v[0]**2 + v[1]**2) #Returning the square of the coordinates. 

def dist (P,Q):

    """ Distance in 2-space.

    Params: 
        P (2-tuple): a point in 2-space
        Q (2-tuple): another point in 2-space
    Returns: (float) dist (P,Q)
    """
    return math.sqrt((Q[0]-P[0]) + (Q[1] - P[1])) #Returning two point's lengths added.

def pathLength2d (pt):

    """Length of a 2-dimensional path.

    Standard length as measured by a ruler.

    Params: pt (list of 2-tuples): path in 2-space
    Returns: (float) length of this path
    """
    
    newNumber = 0 #Saving my answer into a new value.
    for i in range(len(pt)): #Iterate over the length of the tuple. 
        newNumber += dist(pt[0],pt[-1]) #I add the first and last coordinate of the tuple using the formula.
    return math.sqrt(newNumber) #Now that I think about it, this sqrt probably shouldn't be here...


print (pathLength2d ([(0,0), (1,1)])) #Root of 2

---

Solved it. I overthought the program a ton.

[Ofnuts]

Python will very simply parse out everything for you (this is called 'unpacking'). Of course this only works for fixed-length items but his is the case here.

>>> (x1,y1),(x2,y2)=[(0,1), (2,3)]
>>> print x1,y1,x2,y2
0 1 2 3