An mp_int structure is usable only if mp_init() returns MP_OKAY; mp_init() may return MP_MEM if it fails to allocate memory (see https://github.com/libtom/libtommath/blob/v1.2.0/bn_mp_init.c#L12).

mp_init() must be checked to avoid a warning when compiling against standalone libtommath headers (rather than Tcl-bundled libtommath):

./Modules/_tkinter.c:908:5: warning: ignoring return value of function declared with 'warn_unused_result' attribute [-Wunused-result]
    mp_init(&bigValue);
    ^~~~~~~ ~~~~~~~~~
1 warning generated.

Linked PRs

• gh-106350: do not ignore return value of mp_init() #106351
• [3.12] gh-106350: Tkinter: do not ignore return value of mp_init() (GH-106351) #107258
• [3.11] gh-106350: Tkinter: do not ignore return value of mp_init() (GH-106351) #107259