On 07Apr2015 15:43, kai.pet...@gmail.com <kai.pet...@gmail.com> wrote:
I just wrote this bit (coming from Pascal) and am wondering how seasoned Python
programmers would have done the same? Anything terribly non-python?
As always, thanks for all input.
K
"""
Creates a PNG image from EPD file
"""
import os, sys
from PIL import Image, ImageFont, ImageDraw
# -----------------------------------------------------------------------------
def RenderByte(draw, byte, x, y):
blist = list(bin(byte).lstrip('0b')) # turn byte into list with 8 elements,
Remark: .lstrip does not do what you think.
You want:
blist = list(bin(byte)[2:]) # turn byte into list with 8 elements,
to skip over the leading "0b". Otherwise, with lstrip, consider what would
happen with a low value byte, with multiple leading zeroes. (Actually, on
reflection, you might get away with it - but probably not, and anyway would be
fragile against changing the ordering of the bits.)
I'd be popping off the least or most siginificant bit myself with "&" and "<<"
or ">>". It might be wordier, bit it would be more in keeping with the actual
bitwise operations going on.
c = 0 # each representing one bit
for bit in blist:
if bit:
draw.point((x + c, y), fcolor)
c += 1
This might be more Pythonic written:
for c, bit in enumerate(blist):
which will emit (0, b0), (1, b1) and so forth for bit 0, bit 1 etc (where bit 0
is the leftmost from your list, etc). Avoids the "c = 0" and the "c += 1" and
also makes your loop robust against adding control flows later which might skip
the final "c += 1" at the end, even by accident.
return
You generally do not need a trailing return with no value; it is implicit.
def EPD_2_Image(edpfilename, imagefilename):
# get out of here if EPD file not present
if not os.path.isfile(epdfilename):
print 'file not found: ' + edpfilename
return
Traditionally one would raise an exception instead of returning. Eg:
if not os.path.isfile(epdfilename):
raise ValueError("missing file: %r" % (epdfilename,))
and have the caller handle the issue. Similarly for all the other pre-checks
below.
Also, it is normal for error messages to be directed to sys.stderr (this allows
them to be logged independently of the program's normal output; for example the
normal output might be sent to a file, but the error messages would continue to
be displayed on screen). So were you to iussue a print statement (instead of an
exception) you would write:
print >>sys.stderr, ....
or in Python 3:
print(...., file=sys.stderr)
# is this a valid EPD file?
filesize = os.path.getsize(epdfilename)
if (((xdim / 8) * ydim) + header) <> filesize:
print 'incorrect file size: ' + edpfilename
return
# blow old destination file away
if os.path.isfile(imagefilename):
print 'deleting old dest. file: ' + imagefilename
os.remove(imagefilename)
print 'processing...'
# set up PIL objects
img = Image.new('1', (xdim, ydim), bcolor) # '1' = Bi-tonal image
draw = ImageDraw.Draw(img)
# read entire EPD file into byte array (without the header)
content = bytearray(open(epdfilename, 'rb').read())[16:]
# image coord origin at top/left according to PIL documentation
pos = 0
for y in range(ydim):
x = 0
for byte in range(xdim / 8): # 8 pixels 'stuffed' into one byte
RenderByte(draw, content[pos], x, y)
pos += 1
x += 8
img.save(imagefilename) # format is inferred from given extension
print 'done.'
return
Again, this "return" can be implicit.
# -----------------------------------------------------------------------------
xdim = 1024
ydim = 1280
header = 16
black = 0
white = 1
bcolor = black
fcolor = white
epdfilename = 'c:\\temp\\drawtest2.epd'
imagefilename = 'c:\\temp\\drawtest2.png'
Normally these values would be at the top of your program, and named in
UPPER_CASE to indicate that they are like "constants" in other languages. So
you might put this:
XDIM = 1024
YDIM = 1280
HEADER_SIZE = 16
BLACK = 0
WHITE = 1
BCOLOR = BLACK
FCOLOR = WHITE
EPD_FILENAME = 'c:\\temp\\drawtest2.epd'
IMAGE_FILENAME = 'c:\\temp\\drawtest2.png'
at the top of the script.
I notice you have a bare [16:] in your "content =" line. Should that not say
"[HEADER_SIZE:]" ?
EPD_2_Image(epdfilename, imagefilename)
I tend to write things like this as thought they could become python modules
for reuse. (Often they do; why write something twice?)
So the base of the script becomes like this:
if __name__ == '__main__':
EPD_2_Image(EPD_FILENAME, IMAGE_FILENAME)
In this way, when you invoke the .py file directly __name__ is "__main__" and
your function gets run. But it you move this all into a module which may be
imported, __name__ will be the module name, an so not invoke the main function.
The importing code can then do so as it sees fit.
Cheers,
Cameron Simpson <c...@zip.com.au>
I heard a funny one this weekend. I was belaying a friend on a very short
problem and when she was pumped out she told me to "Let me down" and my
other friend that was standing nearby said. "You were never UP!".
- Bryan Laws <bryanl...@aol.com>
--
https://mail.python.org/mailman/listinfo/python-list
