Size of disk/partition in Python is different than linux command

Using: Python 3.7.6 , OS Linux (rmp)

I need to extract total and free sizes of disks and partitions in Python.

I tried different Python functions to retrieve block size in bytes (the results were the same). Then I compared to results of Linux commands (also in bytes), results were different (Linux commands different than Python).

Python functions:

1. Using os.statvfs

import os 
statvfs  = os.statvfs('/dev/sda')     
statvfs.f_frsize *statvfs.f_blocks   
statvfs.f_frsize * statvfs.f_bfree

Results:
size of /dev/sda is 1973968896
size of /dev/sda1 is 1973968896 (the same??!)

2. Using shutil.disk_usage :

print(shutil.disk_usage('/dev/sda'))
usage(total=1973968896, used=0, free=1973968896)

print(shutil.disk_usage('/dev/sda1') )
usage(total=1973968896, used=0, free=1973968896)

I tried also psutil:

import psutil
print(psutil.disk_usage('/dev/sda'))
print(psutil.disk_usage('/dev/sda1'))
same results as 1. and 2.

Linux command:

1. blockdev –getsize64 #Print device size in bytes

blockdev --getsize64 /dev/sda
8001563222016

blockdev --getsize64 /dev/sda1
80014737408

2. lsblk -b

What do I miss here ? Why Python results are different than Linux command (while all units in bytes)? Why Python sizes of sda and sda1 are the same ?

Answer

Both https://docs.python.org/3/library/shutil.html#shutil.disk_usage and https://docs.python.org/3/library/os.html#os.statvfs are used to get stats on filesystem and not a block device, so when you are using /dev/sda or /dev/sda1 as argument – you are actually getting info about /dev

You can get similar results with stat command, here is example with my /dev/sdb.

In python:

print(shutil.disk_usage('/dev/sdb'))                                                                                                                                                
usage(total=8324083712, used=0, free=8324083712)

print(shutil.disk_usage('/dev'))                                                                                                                                                
usage(total=8324083712, used=0, free=8324083712)

In shell:

LANG=C stat -f /dev/sdb   
  File: "/dev/sdb"
    ID: 0        Namelen: 255     Type: tmpfs
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 2032247    Free: 2032247    Available: 2032247
Inodes: Total: 2032247    Free: 2031625

LANG=C stat -f /dev/   
  File: "/dev/"
    ID: 0        Namelen: 255     Type: tmpfs
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 2032247    Free: 2032247    Available: 2032247
Inodes: Total: 2032247    Free: 2031625

echo $(( 2032247 * 4096 ))
8324083712

You can see that shutil output and block size * blocks total are exactly the same.

Notice the -f flag:

-f, --file-system display file system status instead of file status