examples | Python Fiddle

import io

#f = io.StringIO('''6
#0 0
#40 0
#80 0
#0  30
#40 30
#80 30
#''')

#N =int(f.readline())  
#A = [[ int(j) for j in f.readline().split() ] for i in range(N) ]
#N = 9
#A = [(0,0),(40,0),(80,0),(0,30),(40,30),(80,30),(0,60),(40,60),(80,60)]
N = 4
A = [(0,0),(0,100),(100,0),(50,50)]

A.sort()

from math import sqrt 
def dist(t1,t2):
    global A
    x1,y1 = A[t1]
    x2,y2 = A[t2]
    d1 = sqrt((y2-y1)*(y2-y1)+(x2-x1)*(x2-x1))
    if debug & 2: print("(%d, %d) = %0.2f" % (t1+1, t2+1, d1))
    return d1

def lines(b, e):
    global A
    flg = 0
    for i in range(b+1, e):
        x1,y1 = A[b]
        x2,y2 = A[i]    
        x3,y3 = A[e]
        if abs( (y2-y1)*float(x3-x1)- (y3-y1)*float(x2-x1) ) < 0.0001:
           if debug &4: print("(%d ->%d->%d) = Lines" % (b+1, i+1, e+1))
           flg = 1
           break
    return flg

debug = 7  # 0..7 (1:A,2:dist,4:lines        
if debug & 1:
    for (key, value) in enumerate(A,1):
    	print('%d:%s' % (key, value))
res = 0
        
for i in range(N-1):
    for j in range(i+1,N):
        if not lines(i,j):
            res = res + dist(i,j)
            
print("%d" % res )

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