Python text with alpha channel background

Question

I'm working with Python 2.7.3 and PIL/Pillow and want to create text (with opacity) on an alpha_channel background saved as png. Here is my code which doesn't do exactly, what I was hoping:

from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
from PIL import ImageEnhance

width=854
height=480
opacity=0.8
text='copyright'
filename = 'result.png'
black = (0,0,0)
white = (255,255,255)

font = ImageFont.truetype('verdana.ttf',15)
wm = Image.new('RGBA',(width,height),white)
im = Image.new('L',(width,height),0)

draw = ImageDraw.Draw(wm)
w,h = draw.textsize(text, font)
draw.text(((width-w)/2,(height-h)/2),text,white,font)

en = ImageEnhance.Brightness(wm)
#en.putalpha(mask)
mask = en.enhance(1-opacity)
im.paste(wm,(25,25),mask)

im.save(filename)

Result:

The following code is what I'm looking for, but the background fully transparent/alpha_channel:

import PIL
from PIL import ImageFont
from PIL import Image
from PIL import ImageDraw

width = 854
height = 480
black = (0,0,0)
text = "copyright"
white = (255,255,255)
font = ImageFont.truetype("Arial.ttf",40)
img = Image.new("RGBA", (width,height),white)
draw = ImageDraw.Draw(img)
w, h = draw.textsize(text, font)
draw.text(((width-w)/2,(height-h)/2),text,black,font=font)
draw = ImageDraw.Draw(img)
#img.putalpha
img.save("result.png")
#img.show

Result:

Answer 1

The problem is that wm has the same color as the text, so you won't see anything if you draw the text onto it. Change the color of wm to transparent, like I did below (and remove the commas after initializing of width, height and opacity):

from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
from PIL import ImageEnhance

width=854
height=480
opacity=0.8
text='copyright'
filename = 'result.png'
black = (0,0,0)
white = (255,255,255)
transparent = (0,0,0,0)

font = ImageFont.truetype('verdana.ttf',15)
wm = Image.new('RGBA',(width,height),transparent)
im = Image.new('RGBA',(width,height),transparent) # Change this line too.

draw = ImageDraw.Draw(wm)
w,h = draw.textsize(text, font)
draw.text(((width-w)/2,(height-h)/2),text,white,font)

en = ImageEnhance.Brightness(wm)
#en.putalpha(mask)
mask = en.enhance(1-opacity)
im.paste(wm,(25,25),mask)

im.save(filename)