Bash script to select a single Python function from a file

Question

For a git alias problem, I'd like to be able to select a single Python function from a file, by name. eg:

  ...
  def notyet():
      wait for it

  def ok_start(x):
      stuff
      stuff
      def dontgettrickednow():
         keep going
  #stuff
      more stuff

  def ok_stop_now():

In algorithmic terms, the following would be close enough:

1. Start filtering when you find a line that matches /^(\s*)def $1[^a-zA-Z0-9]/
2. Keep matching until you find a line that is not ^\s*# or ^/\1\s] (that is, either a possibly-indented comment, or an indent longer than the previous one)

(I don't really care if decorators before the following function are picked up. The result is for human reading.)

I was trying to do this with Awk (which I barely know) but it's a bit harder than I thought. For starters, I'd need a way of storing the length of the indent before the original def.

Answer 1

Why not just let python do it? I think the inspection module can print out the source of a function, so you could just import the module, select the function and inspect it. Hang on. Banging away at a solution for you...

OK. It turns out the inspect.getsource function doesn't work for stuff defined interactively:

>>> def test(f):
...     print 'arg:', f
...
>>> test(1)
arg: 1
>>> inspect.getsource(test)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\inspect.py", line 699, in getsource
    lines, lnum = getsourcelines(object)
  File "C:\Python27\lib\inspect.py", line 688, in getsourcelines
    lines, lnum = findsource(object)
  File "C:\Python27\lib\inspect.py", line 529, in findsource
    raise IOError('source code not available')
IOError: source code not available
>>>

But for your use case, it will work: For modules that are saved to disk. Take for instance my test.py file:

def test(f):
    print 'arg:', f

def other(f):
    print 'other:', f

And compare with this interactive session:

>>> import inspect
>>> import test
>>> inspect.getsource(test.test)
"def test(f):\n    print 'arg:', f\n"
>>> inspect.getsource(test.other)
"def other(f):\n    print 'other:', f\n"
>>>

So... You need to write a simple python script that accepts the name of a python source file and a function/object name as arguments. It should then import the module and inspect the function and print that to STDOUT.

Answer 2

One way using awk. Code is well commented, so I hope it's easy to understand.

Content of infile:

  ...
  def notyet():
      wait for it

  def ok_start(x):
      stuff
      stuff
      def dontgettrickednow():
         keep going
  #stuff
      more stuff

  def ok_stop_now():

Content of script.awk:

BEGIN {
        ## 'f' variable is the function to search, set a regexp with it.
        f_regex = "^" f "[^a-zA-Z0-9]"

        ## When set, print line. Otherwise omit line.
        ## It is set when found the function searched.
        ## It is unset when found any character different from '#' with less
        ## spaces before it.
        in_func = 0
}

## Found function.
$1 == "def" && $2 ~ f_regex {

        ## Get position of first 'd' in the line.
        i = index( $0, "d" )

        ## Sanity check. Never should success because the condition was
        ## checked before.
        if ( i == 0 ) {
                next
        }

        ## Get characters until matched index before, check that all of
        ## them are spaces, and get its length.
        indent = substr( $0, 0, i - 1 )
        if ( indent ~ /^[[:space:]]*$/ ) {
                num_spaces = length( indent )
        }

        ## Set variable, print line and read next one.
        in_func = 1
        print
        next
}

## When we are inside the function, line doesn't begin with '#' and
## it's not a blank line (only spaces).
in_func == 1 && $1 ~ /^[^#]/ && $0 ~ /[^[:space:]]/ {

        ## Get how many characters there are until first non-space. The result
        ## is the position of first non-blank, so substract one to get the number
        ## of spaces.
        spaces = match( $0, /[^[:space:]]/ )
        spaces -= 1

        ## If current indent is less or equal that the indent of function definition, then
        ## end of function found, so end processing.
        if ( spaces <= num_spaces ) {
                in_func = 0
        }
}

## Self-explanatory.
in_func == 1 { 
        print
}

Run it like:

awk -f script.awk -v f="ok_start" infile

With following output:

  def ok_start(x):
      stuff
      stuff
      def dontgettrickednow():
         keep going
  #stuff
      more stuff