FAQ
Hi all,

reading Dive Into Python, on Chapter 6 (exception), I've found:

"This code comes from the getpass module, a wrapper module for getting a
password from the user"

try:
import termios, TERMIOS
except ImportError:
try:
import msvcrt
except ImportError:
try:
from EasyDialogs import AskPassword
except ImportError:
getpass = default_getpass
else:
getpass = AskPassword
else:
getpass = win_getpass
else:
getpass = unix_getpass

Knowing that this code is very simple, my question is about simplicity. I
think it is simpler the following code. I haven't a long experience on
Python, so I'd like to know your opinions about.

try:
import termios, TERMIOS
getpass = unix_getpass

except ImportError:
try:
import msvcrt
getpass = win_getpass

except ImportError:
try:
from EasyDialogs import AskPassword
getpass = AskPassword

except ImportError:
getpass = default_getpass

thanks,
Fabio

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  • Steve Holden at Aug 12, 2007 at 5:49 pm

    Fabio Z Tessitore wrote:
    Hi all,

    reading Dive Into Python, on Chapter 6 (exception), I've found:

    "This code comes from the getpass module, a wrapper module for getting a
    password from the user"

    try:
    import termios, TERMIOS
    except ImportError:
    try:
    import msvcrt
    except ImportError:
    try:
    from EasyDialogs import AskPassword
    except ImportError:
    getpass = default_getpass
    else:
    getpass = AskPassword
    else:
    getpass = win_getpass
    else:
    getpass = unix_getpass

    Knowing that this code is very simple, my question is about simplicity. I
    think it is simpler the following code. I haven't a long experience on
    Python, so I'd like to know your opinions about.

    try:
    import termios, TERMIOS
    getpass = unix_getpass

    except ImportError:
    try:
    import msvcrt
    getpass = win_getpass

    except ImportError:
    try:
    from EasyDialogs import AskPassword
    getpass = AskPassword

    except ImportError:
    getpass = default_getpass
    In matters of style such as this there *are* only opinions. I don't
    think there are definite grounds for preferring either one.

    If you were to propose such a patch on the python-dev list, it would
    almost certainly be rejected - not because it is necessarily worse, but
    because it would represent a change of style only.

    regards
    Steve
    --
    Steve Holden +1 571 484 6266 +1 800 494 3119
    Holden Web LLC/Ltd http://www.holdenweb.com
    Skype: holdenweb http://del.icio.us/steve.holden
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  • Fabio Z Tessitore at Aug 12, 2007 at 6:01 pm

    Il Sun, 12 Aug 2007 13:49:18 -0400, Steve Holden ha scritto:
    In matters of style such as this there *are* only opinions. I don't
    think there are definite grounds for preferring either one.
    Opinions are what I'd like to see, because most of you have bigger
    experience than me. maybe this example is too trivial for that ... ;-)

    If you were to propose such a patch on the python-dev list,
    Oh no, I didn't think that

    thanks,

    bye
    Fabio
  • Peter Otten at Aug 12, 2007 at 6:06 pm

    Fabio Z Tessitore wrote:

    reading Dive Into Python, on Chapter 6 (exception), I've found:

    "This code comes from the getpass module, a wrapper module for getting a
    password from the user"
    ????????????????try:
    ????????????????????????from EasyDialogs import AskPassword
    ????????????????except ImportError:
    ????????????????????????getpass = default_getpass
    ????????????????else:
    ????????????????????????getpass = AskPassword
    Knowing that this code is very simple, my question is about simplicity. I
    think it is simpler the following code. I haven't a long experience on
    Python, so I'd like to know your opinions about.
    ????????????????try:
    ????????????????????????from EasyDialogs import AskPassword
    ????????????????????????getpass = AskPassword
    ????????????????except ImportError:
    ????????????????????????getpass = default_getpass
    I think you are asking the wrong question. The difference between these two
    functionally equivalent snippets is in expressiveness rather than
    simplicity.

    The first can be read as

    try:
    <operation that may fail>
    except <Error I can handle>:
    <fix it>
    else:
    <build on successful operation>

    When you move the else suite into the try...except

    try:
    <operation that may fail>
    <build on successful operation> #
    except <Error I can handle>:
    <fix it>

    you blur the difference between <operation that may fail> and <build on
    successful operation> while at the same time introducing the implicit
    constraint that the latter does not fail with <Error I can handle>.
    Therefore the original code gives the reader a much clearer notion of the
    author's intention. This may not be a problem for the simple code at hand
    but is definitely a bad habit to get into.

    Peter
  • Fabio Z Tessitore at Aug 12, 2007 at 6:18 pm
    Il Sun, 12 Aug 2007 20:06:23 +0200, Peter Otten ha scritto:

    [cut]
    at the same time introducing the implicit
    constraint that the latter does not fail with <Error I can handle>.
    Therefore the original code gives the reader a much clearer notion of
    the author's intention. This may not be a problem for the simple code
    at hand but is definitely a bad habit to get into.
    thanks Peter, that's the kind of opinion I'm interesting to.

    bye
    Fabio
  • Greg at Aug 13, 2007 at 12:52 am

    Peter Otten wrote:
    try:
    <operation that may fail>
    except <Error I can handle>:
    <fix it>
    else:
    <build on successful operation>

    When you move the else suite into the try...except

    try:
    <operation that may fail>
    <build on successful operation> #
    except <Error I can handle>:
    <fix it>
    Note that in general the semantics of these are different,
    since in the first version the except clause will only catch
    exceptions in <operation that may fail>, whereas in the
    second it may catch exceptions in <build on successful operation>
    as well.

    It probably doesn't make a difference in this example, but
    there are situations where it can.

    --
    Greg

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postedAug 12, '07 at 5:16p
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