python - How to draw a line of characters in a grid (nested lists) -

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given w x h sized grid, produced in following way

self.grid = [ ['-'] * self.w ] * self.h

i wish "draw" "line" of characters between 2 points in said grid. following code i've come with

def line( self, char, (x1, y1), (x2, y2) ):     self.point( char, (x1, y1) )      x = x1 + cmp( x2, x1 )     y = y1 + cmp( y2, y1 )     while x != x2 or y != y2:         self.point( char, (x, y) )         x = x + cmp( x2, x )         y = y + cmp( y2, y )      self.point( char, (x2, y2) )

where point() function fills in single point in grid char.

this works charm straight lines , perfect diagonals. works "crooked" lines too, in sense doesn't throw errors, doesn't line between 2 points, more like... don't know, hockey stick.

for example, given 10x7 grid , call

line( 'x', (1,1), (5,9) )

i get

---------- -x-------- --x------- ---x------ ----x----- -----xxxxx ----------

what i'd more like

---------- -x-------- ---x------ -----x---- -------x-- ---------x ----------

how this, while not breaking straight lines , perfect diagonals in process? need 2 distinct pieces of code handle 2 cases, or can 1 algorithm both?

you should using bresenham's line algorithm, if insist on programming @ all. furthermore, careful initialising grid this:

grid = [ ['-'] * self.w ] * self.h

because of edning self.h copies of same list:

grid = [ ['-'] * 3 ] * 3  grid[0][0] = 'x' print grid # [['x', '-', '-'], ['x', '-', '-'], ['x', '-', '-']]

use

grid = [['-'] * self.w ignored in xrange(self.h)]

or numpy arrays instead.


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