Antoine Pitrou added the comment:
I'm not sure it is good practice to read that many bytes from /dev/urandom.
Quoting the Linux man page for /dev/urandom:
The kernel random-number generator is designed to produce a small
amount of
high-quality seed material to seed a cryptographic pseudo-random number
gen‐
erator (CPRNG). It is designed for security, not speed, and is
poorly
suited to generating large amounts of random data. Users should be
very
economical in the amount of seed material that they read from
/dev/urandom
(and /dev/random); unnecessarily reading large quantities of data from
this
device will have a negative impact on other users of the device.
The (default?) entropy pool size under Linux is 4096 bytes, so reading 2500
bytes will deplete more than half of it, IIUC. Example:
$ cat /proc/sys/kernel/random/poolsize
4096
$ cat /proc/sys/kernel/random/entropy_avail
516
$ python -c "import os; os.urandom(300)"
$ cat /proc/sys/kernel/random/entropy_avail
160
----------
nosy: +neologix, pitrou
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