I use GIMP to help me find colors for my webpages. But GIMP colors are in base 10 while HTML uses base 16. I got tired of doing the conversions by hand so I wrote a pair of simple Python programs called 2hex.py and hex2.py. While writing this code, I had a familiar experience: trouble finding what I wanted in documentation. Python documentation is some of the best around, but these problems still occur. Here is the tale:
It is easy to convert an integer into a string in hex format.
i = 123 print i, hex(i), '%X' % iBut how do I convert a string in hex format into an integer? First I try
try: i = int('0x3a') except Exception, x: print str(x)Perhaps the built-in function
hexhas an opposite. I go to Library Reference, 2.2 Built-in Functions and find nothing. Next I use the UNIX utility grep to search all the documentation text for the letters "
hex". Nothing. I remember the C function atoi. I remember that Python has this function in module
string. There I find "(Also note: for a more flexible interpretation of numeric literals, use the built-in function eval().)" Problem solved. I was in the wrong mental space.
s = '0x3a' print eval(s)The only thing of interest in this story is the process. I know a collection of facts about some system. I use these facts to try to uncover another fact. If I succeed, I either write down a note somewhere or memorize a new fact. The more I know about a system, the easier this process is. Imagine the pain I went through the first time I installed Linux: where are the X configuration files for RedHat 4.2? And I didn't know the word "configuration"!
I would be helped by (automatically generated) keyword links. Click on a
little icon at the documentation for
hex() and find all other
places in the documentation where the words "hexadecimal", "literal",
"OverflowError", etc. occur. In some cases, sets of associated words will
need to be input into the code that generates the links. For example,
"hexadecimal <--> base".
These sets of associated words can be useful in a broader context. Suppose I want to answer the question "How do I write programs that do things with images?" by searching the Internet. Once I find the first magic phrase, say "image processing", I probably can find others, "computer vision", "image understanding", "machine vision", "medical imaging", etc. Here are some further examples:
hex(). As I wrote this, I searched comp.lang.python
for "hex OR literal OR "word size" OR OverflowError" trying to locate
questions about hex(). The results included:
import string string.atoi(hex(150),0) eval('0xf') string.atoi('0xf', 16)and a _lot_ of other stuff. It might be useful to embed canned news article searches into the documentation. Is there a better search string to use? Is there any software that can help eliminate irrelevent answers?
Here are the little programs 2hex.py and hex2.py.
#=== 2hex.py ================================================== import sys if len(sys.argv) < 2: raise Exception, 'Must have at least one argument.' for i in range(1, len(sys.argv)): print '%X' % int(sys.argv[i]), print #=== hex2.py ================================================== import sys if len(sys.argv) < 2: raise Exception, 'Must have at least one argument.' for i in range(1, len(sys.argv)): print eval('0x' + sys.argv[i]), printThe following one line shell file has helped me a lot:
grep $1 /usr/doc/python-2.1/*/*.htmlEdit this to match your system.