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The standard library comes with a number of modules that can be used both as modules and as command-line utilities.

The dis Module

The dis module is the Python disassembler. It converts byte codes to a format that is slightly more appropriate for human consumption.

Example

import dis def sum(): vara = 10 varb = 20 sum = vara + varb print ("vara + varb = %d" % sum) # Call dis function for the function. dis.dis(sum)

This would produce the following result −

  3           0 LOAD_CONST               1 (10)
              2 STORE_FAST               0 (vara)

  4           4 LOAD_CONST               2 (20)
              6 STORE_FAST               1 (varb)

  6           8 LOAD_FAST                0 (vara)
             10 LOAD_FAST                1 (varb)
             12 BINARY_ADD
             14 STORE_FAST               2 (sum)

  7          16 LOAD_GLOBAL              0 (print)
             18 LOAD_CONST               3 ('vara + varb = %d')
             20 LOAD_FAST                2 (sum)
             22 BINARY_MODULO
             24 CALL_FUNCTION            1
             26 POP_TOP
             28 LOAD_CONST               0 (None)
             30 RETURN_VALUE

The pdb Module

The pdb module is the standard Python debugger. It is based on the bdb debugger framework.

You can run the debugger from the command line (type n [or next] to go to the next line and help to get a list of available commands) −

Example

Before you try to run pdb.py, set your path properly to Python lib directory. So let us try with above example sum.py −

$pdb.py sum.py > /test/sum.py(3)<module>() -> import dis (Pdb) n > /test/sum.py(5)<module>() -> def sum(): (Pdb) n >/test/sum.py(14)<module>() -> dis.dis(sum) (Pdb) n 6 0 LOAD_CONST 1 (10) 3 STORE_FAST 0 (vara) 7 6 LOAD_CONST 2 (20) 9 STORE_FAST 1 (varb) 9 12 LOAD_FAST 0 (vara) 15 LOAD_FAST 1 (varb) 18 BINARY_ADD 19 STORE_FAST 2 (sum) 10 22 LOAD_CONST 3 ('vara + varb = %d') 25 LOAD_FAST 2 (sum) 28 BINARY_MODULO 29 PRINT_ITEM 30 PRINT_NEWLINE 31 LOAD_CONST 0 (None) 34 RETURN_VALUE --Return-- > /test/sum.py(14)<module>()->None -v dis.dis(sum) (Pdb) n --Return-- > <string>(1)<module>()->None (Pdb)

The profile Module

The profile module is the standard Python profiler. You can run the profiler from the command line −

Example

Let us try to profile the following program −

vara = 10 varb = 20 sum = vara + varb print "vara + varb = %d" % sum

Now, try running cProfile.py over this file sum.py as follow −

$cProfile.py sum.py vara + varb = 30 4 function calls in 0.000 CPU seconds Ordered by: standard name ncalls tottime percall cumtime percall filename:lineno 1 0.000 0.000 0.000 0.000 <string>:1(<module>) 1 0.000 0.000 0.000 0.000 sum.py:3(<module>) 1 0.000 0.000 0.000 0.000 {execfile} 1 0.000 0.000 0.000 0.000 {method ......}

The tabnanny Module

The tabnanny module checks Python source files for ambiguous indentation. If a file mixes tabs and spaces in a way that throws off indentation, no matter what tab size you're using, the nanny complains.

Example

Let us try to profile the following program −

vara = 10 varb = 20 sum = vara + varb print "vara + varb = %d" % sum

If you would try a correct file with tabnanny.py, then it won't complain as follows −

$tabnanny.py -v sum.py
'sum.py': Clean bill of health.



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