Backport PR
#10788: None
The filename was generated taking the last digits of a randomly
generated number between 0 and 1, if the number is small enough, it's
repr ends with `e-5`, or less (the probability is actually close to
1/1000 because the biggest number we can get with e-5 is (1e-4 -
epsilon).
We actually did hit that on our CI:
-
https://ci.appveyor.com/project/IPython/ipython/build/1.0.839/job/mk4l08s295ynkfs5
```
======================================================================
ERROR: test_run_submodule_with_absolute_import (IPython.core.tests.test_run.TestMagicRunWithPackage)
----------------------------------------------------------------------
Traceback (most recent call last):
File "c:\python36-x64\lib\site-packages\IPython\core\tests\test_run.py", line 455, in test_run_submodule_with_absolute_import
self.check_run_submodule('absolute')
File "c:\python36-x64\lib\site-packages\IPython\core\tests\test_run.py", line 450, in check_run_submodule
self.assertEqual(_ip.user_ns['x'], self.value,
KeyError: 'x'
-------------------- >> begin captured stdout << ---------------------
File "C:\Users\appveyor\AppData\Local\Temp\1\tmp4asmvv33\tmpqpswwe9n\tmp065832886952393e-05\absolute.py", line 2
from tmp065832886952393e-05.sub import x
^
SyntaxError: invalid syntax
```
Actually pick a random string now we should have less chance of being
invalid identifier.
