7.6. Exception Traceback¶
Traceback will help you track down the bug
>>> raise RuntimeError
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError
>>> raise RuntimeError('Huston we have a problem')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: Huston we have a problem
7.6.1. Python 3.11¶
Since Python 3.11
PEP 657 -- Include Fine Grained Error Locations in Tracebacks
Traceback (most recent call last):
File "calculation.py", line 54, in <module>
result = (x / y / z) * (a / b / c)
~~~~~~^~~
ZeroDivisionError: division by zero
Traceback (most recent call last):
File "distance.py", line 11, in <module>
print(manhattan_distance(p1, p2))
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "distance.py", line 6, in manhattan_distance
return abs(point_1.x - point_2.x) + abs(point_1.y - point_2.y)
^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'x'
Traceback (most recent call last):
File "query.py", line 37, in <module>
magic_arithmetic('foo')
File "query.py", line 18, in magic_arithmetic
return add_counts(x) / 25
^^^^^^^^^^^^^
File "query.py", line 24, in add_counts
return 25 + query_user(user1) + query_user(user2)
^^^^^^^^^^^^^^^^^
File "query.py", line 32, in query_user
return 1 + query_count(db, response['a']['b']['c']['user'], retry=True)
~~~~~~~~~~~~~~~~~~^^^^^
TypeError: 'NoneType' object is not subscriptable
7.6.2. Traceback Analysis¶
Stacktrace is 8 levels deep, it's not Java's 200 ;)
Start analysing traceback from bottom-up
Figure 7.2. Stacktrace is 8 levels deep, it's not Java's 200 ;) 1¶
>>> def apollo13():
... raise RuntimeError('Oxygen tank explosion')
>>>
>>>
>>> apollo13()
Traceback (most recent call last):
File "<input>", line 5, in <module>
File "<input>", line 2, in apollo13
RuntimeError: Oxygen tank explosion
>>> def apollo13():
... raise RuntimeError('Oxygen tank explosion')
>>>
>>>
>>> apollo13()
Traceback (most recent call last):
File "/home/watney/myscript.py", line 5, in <module>
apollo13()
File "/home/watney/myscript.py", line 2, in apollo13
raise RuntimeError('Oxygen tank explosion')
RuntimeError: Oxygen tank explosion
>>> def apollo13():
... raise RuntimeError('Oxygen tank explosion')
>>>
>>>
>>> apollo13()
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "/Applications/PyCharm 2021.1 EAP.app/Contents/helpers/pydev/_pydev_bundle/pydev_umd.py", line 197, in runfile
pydev_imports.execfile(filename, global_vars, local_vars) # execute the script
File "/Applications/PyCharm 2021.1 EAP.app/Contents/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
exec(compile(contents+"\n", file, 'exec'), glob, loc)
File "/home/watney/myscript.py", line 4, in <module>
apollo13()
File "/home/watney/myscript.py", line 2, in apollo13
raise RuntimeError('Oxygen tank explosion')
RuntimeError: Oxygen tank explosion
7.6.3. Change Verbosity Level¶
Change level with
sys.tracebacklimitFrom time to time you can have problems somewhere in the middle, but it's rare
Last lines are the most important, in most cases error is there
>>> import sys
>>> sys.tracebacklimit = 2
>>>
>>>
>>> def apollo13():
... raise RuntimeError('Oxygen tank explosion')
>>>
>>>
>>> apollo13()
Traceback (most recent call last):
File "/home/watney/myscript.py", line 4, in <module>
apollo13()
File "/home/watney/myscript.py", line 2, in apollo13
raise RuntimeError('Oxygen tank explosion')
RuntimeError: Oxygen tank explosion
