In Python, why do warnings not appear when using `eval`?

Question

The following code prints a warning, as expected:

>>> import warnings
>>> def f():
...     warnings.warn('Deprecated', DeprecationWarning)
...     print('In function f()')
... 
>>> f()
__main__:2: DeprecationWarning: Deprecated
In function f()

However, when using eval, the warning message does not appear:

>>> eval('f()')
In function f()

Why do warnings behave differently in these two situations?

Answer 1

Why do warnings behave differently in these two situations?

They don't. From the docs:

Repetitions of a particular warning for the same source location are typically suppressed.

import warnings

def f():
    warnings.warn("dep", DeprecationWarning)
    print('in f')

f()
warnings.resetwarnings()
eval('f()')

Or:

import warnings

def f():
    warnings.warn("dep", DeprecationWarning)
    print('in f')

# don't call f()
#f()
eval('f()')

Both show the warning from the eval('f()') call:

# with warnings.resetwarnings() between f() and eval('f()')
in f
/home/gir/local/dev/pcws/local/main.py:7: DeprecationWarning: dep
in f
  warnings.warn("dep", DeprecationWarning)
/home/gir/local/dev/pcws/local/main.py:7: DeprecationWarning: dep
  warnings.warn("dep", DeprecationWarning)

# without calling f() directly
/home/gir/local/dev/pcws/local/main.py:5: DeprecationWarning: dep
in f
  warnings.warn("dep", DeprecationWarning)