import math
#input point of observer
x0,y0,z0=raw_input("enter coordinate separated by commas -> ").split(",")
x0,y0,z0=[float(x0),float(y0),float(z0)]

#input point observed

x1,y1,z1=raw_input("enter coordinate of first point separated by commas -> ").split(",")
x1,y1,z1=[float(x1),float(y1),float(z1)]

x2,y2,z2=raw_input("enter coordinate of second point  separated by commas -> ").split(",")
x2,y2,z2=[float(x2),float(y2),float(z2)]

vec1=[x1-x0,y1-y0,z1-z0]
vec2=[x2-x0,y2-y0,z2-z0]

#dot product of vector
num= sum([vec1[i]*vec2[i] for i in range(3)])

deno=math.sqrt(sum([vec1[i]*vec1[i] for i in range(3)])) * math.sqrt(sum([vec2[i]*vec2[i] for i in range(3)]))

angle=round(math.degrees(math.acos(num/deno)),2)

print angle
Pastebin link to program

https://pastebin.com/TpS4qErN