Python Line Intersection

Chris Rebert clp2 at
Fri Apr 9 22:04:19 CEST 2010

On Fri, Apr 9, 2010 at 11:43 AM, John Nagle <nagle at> wrote:
> Chris Rebert wrote:
>> On Fri, Apr 9, 2010 at 8:04 AM, Peyman Askari <peter_peyman_puk at>
>> wrote:
>>> Hello
>>> This is partly Python related, although it might end up being more math
>>> related.
>>> I am using PyGTK (GUI builder for Python) and I need to find the
>>> intersection point for two lines. It is easy to do, even if you only have
>>> the four points describing line segments
>>> ( However, it
>>> requires that you solve for two equations. How can I do this in Python,
>>> either solve equations, or calculating intersection points some other way?
>> Just solve the equations ahead of time by using generic ones.
>> x = (c - b) / (m-n)
>   Actually, you don't want to do it that way, because it fails for vertical
> lines, when m and n go to infinity.

As the programmer said upon seeing a stripe-less zebra:
"Oh no, a special case!"

Excellent catch my good sir; although I will point out that strictly
speaking, you can't put vertical lines into slope-intercept form (but
I should not have forgotten that precondition).

Vertical line test, etc.

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