Is hand-written C faster than Python? Yes, yes it is.

dpkg-S.c

// make CFLAGS=-O2 dpkgs && time ./dpkgs /lib/systemd/systemd

#define _POSIX_C_SOURCE 200809L
#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <dirent.h>
#include <assert.h>
#include <string.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char **argv) {
    const char *needle = argv[1];
    const size_t needle_len = strlen(needle);
    const size_t buf_len = needle_len + 2;
    char *buf = malloc(needle_len + 3);
    sprintf(buf, "\n%s\n", needle);

    int dir = open("/var/lib/dpkg/info", O_DIRECTORY);
    assert(dir);

    DIR *open_dir = fdopendir(dir);
    assert(dir);

    for (struct dirent *ent = readdir(open_dir); ent; ent = readdir(open_dir)) {
        const size_t len = strlen(ent->d_name);
        if (len < 5 || strcmp(ent->d_name + len - 5, ".list")) {
            continue;
        }

        int file = openat(dir, ent->d_name, O_RDONLY);
        assert(file);
        struct stat stat;
        int stat_status = fstat(file, &stat);
        assert(!stat_status);
        char *map = mmap(NULL, stat.st_size, PROT_READ, MAP_SHARED, file, 0);
        assert(map);
        if (memmem(map, stat.st_size, buf, buf_len)) {
            printf("%s\n", ent->d_name);
        }
        munmap(map, stat.st_size);
        close(file);
    }
}