Python learns day 12 debug assertion logging PDB Pdb.set_trace

Debug

The first method is simple and straightforward, which is to print print out the variables that might be problematic:

>>> def foo (s): n= int (s) print ' >>> n =%d '% nreturn 10/n>>> def main (): foo (' 0 ') >>> Main () >>> n = 0Traceback (most recent call last): File "<pyshell#25>", line 1, in <module>main () file " <pyshell#24> ", line 2, in Mainfoo (' 0 ') File" <pyshell#22> ", line 4, in Fooreturn 10/nzerodivisionerror:integ ER division Ormodulo by Zero

　　

Assertion

Where print is used to assist in viewing, you can replace it with an assertion (assert):

>>> def foo (s): N=int (s) assertn!=0, ' n is zero ' return10/n>>> def main (): foo (' 0 ') >>> main () Traceback (most recent): File "<pyshell#37>", line 1, in <module>main () file "<pyshell#36>", Li NE 2, in Mainfoo (' 0 ') File "<pyshell#32>", line 3, in Fooassert n!=0, ' n was zero ' assertionerror:n is zero

　　

Logging

Replacing print with logging is the 3rd way, and the assert ratio, logging does not throw an error, and can be output to a file:

>>> Import Logging>>>logging.basicconfig (level=logging.info) >>> s= ' 0 ' >>> n= Int (s) >>> logging.info (' n=%d '% n) >>> print 10/n Traceback (most recent call last): File "<pyshell#48 > ", Line 1, in <module>print 10/nzerodivisionerror:integer division Ormodulo by Zero

　　

Pdb

The 4th Way is to launch the Python debugger pdb, to let the program run in a single step, and to view the running state at any time.

# Err.pys = ' 0 ' n = Int (s) print 10/n$ python-m pdb err.py>/users/michael/github/sicp/err.py (2) <module> () s = ' 0 '

　　

After starting with the parameter-m PDB, the PDB navigates to the next code to execute, s = ' 0 '. Enter command l to view the code:

(PDB) L

1 # err.py

2-s = ' 0 '

3 n = Int (s)

4 Print 10/n

[EOF]

Enter command N to step through the code:

(PDB) n

>/users/michael/github/sicp/err.py (3) <module> ()

-n = Int (s)

(PDB) n

>/users/michael/github/sicp/err.py (4) <module> ()

Print 10/n

At any time, you can enter the command p variable name to view the variable:

(PDB) P s

' 0 '

(PDB) P n

0

Enter command q to end debugging, exit the program:

(PDB) n

Zerodivisionerror: ' Integer division Ormodulo by Zero '

>/users/michael/github/sicp/err.py (4) <module> ()

Print 10/n

(PDB) Q

Try

This method of debugging through the PDB on the command line is theoretically omnipotent, but it is too cumbersome

Pdb.set_trace ()

This method also uses the PDB, but does not require stepping, we only need to import the PDB, and then, where possible error place a pdb.set_trace (), you can set a breakpoint:

# err.py

Import pdb

s = ' 0 '

n = Int (s)

Pdb.set_trace () # Running to here will automatically pause

print10/n

Running the code, the program will automatically pause in Pdb.set_trace () and go into the PDB debugging environment, you can view the variable with command p, or continue with command C:

$ python err.py

>/users/michael/github/sicp/err.py (7) <module> ()

Print 10/n

(PDB) P n

0

(PDB) C

Traceback (most recent):

File "err.py", line 7, <module>

Print 10/n

Zerodivisionerror:integer Division Ormodulo by Zero

This is much more efficient than a direct-start PDB, but it's also a high-level one.

Python learns day 12 debug assertion logging PDB Pdb.set_trace