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pynoweb

Being a long-time fan of noweb by Norman Ramsey, I recently checked the internet for a Python clone. I detected noweb.py by Jonathan Aquino (jonathan.aquino@gmail.com), (see http://jonaquino.blogspot.com/2010/04/nowebpy-or-worlds-first-executable-blog.html) and gave it a try. While providing basic support for un"tangling" chunks in *.nw files, it missed a "file include" option. My actual task was to write a rather long shell script (Bash) and I wanted to export it to one single file, but manage/edit it in pieces for a better overview.

So, I took the source, twisted it in some places and added simple "file includes" to the syntax.

Current version

The sources for this tool are now available at Bitbucket. Please visit https://bitbucket.org/dirkbaechle/pynoweb for downloading the latest version.

Basic usage

Noweb files are divided into chunks. The "@" sign in the first column of a line starts a new chunk, after it you can add arbitrary text as description. A chunk can also contain a code section where an output file can be extracted from. A piece of code is defined by the "<<tag>>=" marker. The "tag" can be a filename or a string with several words, separated by blanks.

Within a code section you can refer to other defined code sections by using the "<<tag>>" marker (without the trailing "=").

An example:

@

<<output.sh>>=
<<start of file>>
<<end of file>>

@

<<start of file>>=
echo "Hi"

@

<<end of file>>=
echo "there!"

Saving this as file "output.nw" you can extract the defined output chunk "output.sh"

echo "Hi"
echo "there!"

by the command

python noweb.py -Routput.sh output.nw > output.sh

For more infos about noweb's syntax, refer to its manual please.

Extensions

As an extension to this simple replace mechanism, you can include other files during the chunk parsing phase with the "<<file:infile_name>>" marker. It reads the file "infile_name" and adds its contents to the top file. These includes can be nested arbitrarily, but you have to be careful to avoid cyclic dependencies!

Example:

File "main.nw"

@

<<main.sh>>=
#!/bin/sh

<<file:utils.sh>>
<<utility stuff>>

# EOF

File "utils.sh"

@

<<utility stuff>>=
echo "Hi there!"

Calling

python noweb.py -Rmain.sh main.nw > main.sh

results in the output

#!/bin/sh

echo "Hi there!"

# EOF