[Help-bash] What is going on here? Line with multiple < redirects

[Lane Schwartz]

I teach a class that includes intro to Bash. One of my students tried
something I'd never seen before, and I haven't been able to make sense of
how Bash is parsing this (admittedly bizarre) command.

$ ./part3.py < ./part2.py < ./part1.py < sample.txt

In this example, part3.py appears to directly take sample.txt as input, and
part2.py and part1.py appear to not execute.

Any help figuring out what's going on would be appreciated. The complete
steps to reproduce follow:

$ seq 10 > sample.txt

part1.py:

#!/usr/bin/python3
>
>
> import sys
> import os
>
> os.mknod("part1_ran1.txt")
>
> for line in sys.stdin:
>     print("PART1: {}".format(line.strip()))



part2.py:

#!/usr/bin/python3
>
>
> import sys
> import os
>
> os.mknod("part2_ran1.txt")
>
> for line in sys.stdin:
>     print("PART2: {}".format(line.strip()))



part3.py:

#!/usr/bin/python3
>
>
> import sys
> import os
>
> os.mknod("part3_ran1.txt")
>
> for line in sys.stdin:
>     print("PART3: {}".format(line.strip()))



 $  ./part3.py < ./part2.py < ./part1.py < sample.txt

PART3: 1
> PART3: 2
> PART3: 3
> PART3: 4
> PART3: 5
> PART3: 6
> PART3: 7
> PART3: 8
> PART3: 9
> PART3: 10


$ ls

> part1.py  part2.py  part3.py  part3_ran.txt  sample.txt