debug print shortcut?

[John Mudd]

When debugging python, I add print statements such as these.

print 'i=%s' % `i`
print 'foo()=%s' % `foo()`
print 'a,b,c=%s' % `a,b,c`

I just want to dump the value of a variable or expression. But I
don't like having to type the expression twice, everytime. I can
solve this in 'C' with a preprocessor macro. Can it be solved in
python?

John

[Donald 'Paddy' McCarthy]

John Mudd wrote:

When debugging python, I add print statements such as these.

print 'i=%s' % `i`
print 'foo()=%s' % `foo()`
print 'a,b,c=%s' % `a,b,c`

I just want to dump the value of a variable or expression. But I
don't like having to type the expression twice, everytime. I can
solve this in 'C' with a preprocessor macro. Can it be solved in
python?

John

I found this:

def dump(s, glob, loc): .... print "%s = %s\n" % (s, eval(s,glob,loc) )
.... a=55
dump("a",globals(),locals()) a = 55

Cheers, Pad.

[Roel Schroeven]

John Mudd wrote:

When debugging python, I add print statements such as these.

print 'i=%s' % `i`
print 'foo()=%s' % `foo()`
print 'a,b,c=%s' % `a,b,c`

I just want to dump the value of a variable or expression. But I
don't like having to type the expression twice, everytime. I can
solve this in 'C' with a preprocessor macro. Can it be solved in
python?

def printdebug(s):
print '%s = %s' % (s, `eval(s)`)

--
"Codito ergo sum"
Roel Schroeven

[Jeff Epler]

Here's one way. You specify the expression as a string, and the value
or the exception raised is printed.

import sys

def debug(expression, depth=1):
frame = sys._getframe(depth)
locals = frame.f_locals
globals = frame.f_globals
try:
value = eval(expression, globals, locals)
except:
value = sys.exc_info()[1]
print >>sys.stderr, "%r -> %r" % (expression, value)

debug("3+3") '3+3' -> 6 debug("1/0") '1/0' -> <exceptions.ZeroDivisionError instance at 0x00B6E248> def f(): .... y = 3
.... debug("y+1")
.... f() 'y+1' -> 4

Another way would be to pass the result of the expression to debug(),
and use inspect.getsource() to locate the line of code in the caller. I
haven't written this, but usage might look like debug(3+3)

debug(3+3) -> 6

With this approach, exceptions would be propagated, not handled in
debug().

Jeff

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