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edited Nov 10, 2021 at 15:50

Edit:

Another form would be to exclude the else block and roll the nesting into the try-except, essentially implying an "else" should ConnectRegistry not fail:

reg_a_val = reg_b_val = None
try:
    with ConnectRegistry(None, HKLM) as hklm:

        try:
            reg_a_val = _get_a_val(hklm)
        except OSError as err:
            # log failure
        
        try:
            reg_b_val = _get_b_val(hklm)
        except OSError as err:
            # log failure

except OSError as err:
    # log unable to connect to hivekey

This is done because the outer try-except would need to log failure to even access the hiveroot, whereas the inner try-excepts may or may not fail, but we need to continue even if one does fail. Therefore, the question becomes, is nesting a try-except always considered bad practice, or is a case like this perfectly clear?

Edit:

Another form would be to exclude the else block and roll the nesting into the try-except, essentially implying an "else" should ConnectRegistry not fail:

reg_a_val = reg_b_val = None
try:
    with ConnectRegistry(None, HKLM) as hklm:

        try:
            reg_a_val = _get_a_val(hklm)
        except OSError as err:
            # log failure
        
        try:
            reg_b_val = _get_b_val(hklm)
        except OSError as err:
            # log failure

except OSError as err:
    # log unable to connect to hivekey

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asked Nov 9, 2021 at 23:13

pstatix

Is nesting try-except sequence in try-else block bad form?

Ive got a boot sequence that needs to check some registry values, they may or may not be present, so each check needs to be wrapped in its own try-except. I try to avoid nesting as I think it can lead to confusion, but what I ended up with was:

reg_a = reg_b = True
reg_a_val = reg_b_val = None
try:
    hklm = ConnectRegistry(None, HKLM)
except OSError as err:
    # log unable to connect to hivekey
else:
    try:
        reg_a_val = _get_a_val(hklm)
    except OSError as err:
        # log failure
        reg_a = False
    try:
        reg_b_val = _get_b_val(hklm)
    except OSError as err:
        # log failure
        reg_b = False

In an attempt to avoid this, I thought maybe setting a flag prior would reduce:

hklm = None
try:
    hklm = ConnectRegistry(None, HKLM)
except OSError as err:
    # log unable to connect to hivekey

if hklm:
    try:
        reg_a_val = _get_a_val(hklm)
    except OSError as err:
        # log failure
        reg_a = False
    try:
        reg_b_val = _get_b_val(hklm)
    except OSError as err:
        # log failure
        reg_b = False

But I then realized its the same depth as just putting them in the else block.

So which would be preferred? If neither, is there an alternative when subsequent try-except blocks must be used while accessing a variable from a preceding try-except?