Git Guide 2: A Practical Application of Diff and Patch

File with code

#!/usr/bin/env python3

import shutil

def check_disk_usage(disk, min_absolute, min_percent):
    """Returns True if there is enough free disk space, false otherwise."""
    du = shutil.disk_usage(disk)
    # Calculate the percentage of free space
    percent_free = 100 * du.free / du.total
    # Calculate how many free gigabytes
    gigabytes_free = du.free / 2**30
    if percent_free < min_percent or gigabytes_free < min_absolute:
        return False
    return True

# Check for at least 2 GB and 10% free
if not check_disk_usage("/", 2*2**30, 10):
    print("ERROR: Not enough disk space")
    return 1

print("Everything ok")
return 0

Command:

$ cp disk_usage.py disk_usage_original.py 
$ cp disk_usage.py disk_usage_fixed.py 
# this throws an error
$ ./disk_usage_fixed.py 

Code output:

File "./disk_usage_fixed.py", line 19

    return 1

    ^

SyntaxError: 'return' outside function

File with code

Adds import sys at the beginning, then change return 1 to sys.exit(1) and return 0 to sys.exit(0).

#!/usr/bin/env python3

import shutil
import sys

def check_disk_usage(disk, min_absolute, min_percent):
    """Returns True if there is enough free disk space, false otherwise."""
    du = shutil.disk_usage(disk)
    # Calculate the percentage of free space
    percent_free = 100 * du.free / du.total
    # Calculate how many free gigabytes
    gigabytes_free = du.free / 2**30
    if percent_free < min_percent or gigabytes_free < min_absolute:
        return False
    return True

# Check for at least 2 GB and 10% free
if not check_disk_usage("/", 2*2**30, 10):
    print("ERROR: Not enough disk space")
    sys.exit(1)

print("Everything ok")
sys.exit(0)

Command:

$ ./disk_usage_fixed.py

Code output:

ERROR: Not enough disk space

File with code

Change check_disk_usage("/", 2*2**30, 10) in previous file to check_disk_usage("/", 2, 10).Because the code gigabytes_free = du.free / 2**30 changes the value to gigabytes, so don't need to multiply by 2**30.

#!/usr/bin/env python3

import shutil
import sys

def check_disk_usage(disk, min_absolute, min_percent):
    """Returns True if there is enough free disk space, false otherwise."""
    du = shutil.disk_usage(disk)
    # Calculate the percentage of free space
    percent_free = 100 * du.free / du.total
    # Calculate how many free gigabytes
    gigabytes_free = du.free / 2**30
    if percent_free < min_percent or gigabytes_free < min_absolute:
        return False
    return True

# Check for at least 2 GB and 10% free
if not check_disk_usage("/", 2, 10):
    print("ERROR: Not enough disk space")
    sys.exit(1)

print("Everything ok")
sys.exit(0)

Command:

$ ./disk_usage_fixed.py 

Code output:

Everything ok

Command:

$ diff -u disk_usage_original.py disk_usage_fixed.py > disk_usage.diff
$ cat disk_usage.diff 

Code output:

--- disk_usage_original.py	2023-06-22 15:13:38.591579963 -0700

+++ disk_usage_fixed.py	2023-06-22 15:41:35.013023839 -0700

@@ -1,6 +1,7 @@

 #!/usr/bin/env python3

 

 import shutil

+import sys

 

 def check_disk_usage(disk, min_absolute, min_percent):

     """Returns True if there is enough free disk space, false otherwise."""

@@ -14,9 +15,9 @@

     return True

 

 # Check for at least 2 GB and 10% free

-if not check_disk_usage("/", 2*2**30, 10):

+if not check_disk_usage("/", 2, 10):

     print("ERROR: Not enough disk space")

-    return 1

+    sys.exit(1)

 

 print("Everything ok")

-return 0

+sys.exit(0)

Command:

$ patch disk_usage.py < disk_usage.diff 

Code output:

patching file disk_usage.py

Command:

$ ./disk_usage.py 

Code output:

Everything ok