Building the _astrcmp module prints deprecation warnings:

running build_ext
building 'picard.util._astrcmp' extension
creating build/temp.linux-x86_64-3.7
creating build/temp.linux-x86_64-3.7/picard
creating build/temp.linux-x86_64-3.7/picard/util
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -march=x86-64 -mtune=generic -O3 -pipe -fstack-protector-strong -fno-plt -flto=4 -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -march=x86-64 -mtune=generic -O3 -pipe -fstack-protector-strong -fno-plt -march=x86-64 -mtune=generic -O3 -pipe -fstack-protector-strong -fno-plt -fPIC -I/usr/include/python3.7m -c picard/util/_astrcmp.c -o build/temp.linux-x86_64-3.7/picard/util/_astrcmp.o
picard/util/_astrcmp.c: In Funktion »astrcmp«:
picard/util/_astrcmp.c:159:2: Warnung: »PyUnicode_GetSize« ist veraltet [-Wdeprecated-declarations]
len1 = PyUnicode_GetSize(s1);
^~~~
In file included from /usr/include/python3.7m/Python.h:80,
from picard/util/_astrcmp.c:43:
/usr/include/python3.7m/unicodeobject.h:793:24: Anmerkung: hier deklariert
PyAPI_FUNC(Py_ssize_t) PyUnicode_GetSize(
^~~~~~~~~~~~~~~~~
picard/util/_astrcmp.c:160:2: Warnung: »PyUnicode_GetSize« ist veraltet [-Wdeprecated-declarations]
len2 = PyUnicode_GetSize(s2);
^~~~
In file included from /usr/include/python3.7m/Python.h:80,
from picard/util/_astrcmp.c:43:
/usr/include/python3.7m/unicodeobject.h:793:24: Anmerkung: hier deklariert
PyAPI_FUNC(Py_ssize_t) PyUnicode_GetSize(
^~~~~~~~~~~~~~~~~
creating build/lib.linux-x86_64-3.7
creating build/lib.linux-x86_64-3.7/picard
creating build/lib.linux-x86_64-3.7/picard/util
gcc pthread -shared -Wl,-O1,sort-common,as-needed,-z,relro,-z,now -flto=4 -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -Wl,-O1,sort-common,-as-needed,-z,relro,-z,now build/temp.linux-x86_64-3.7/picard/util/_astrcmp.o -L/usr/lib -lpython3.7m -o build/lib.linux-x86_64-3.7/picard/util/_astrcmp.cpython-37m-x86_64-linux-gnu.so
copying build/lib.linux-x86_64-3.7/picard/util/_astrcmp.cpython-37m-x86_64-linux-gnu.so -> picard/util