Cara menggunakan python raise different exception

Exception Kelas dasar untuk semua pengecualian / exception StopIteration Dibesarkan ketika metode (iterator) berikutnya dari iterator tidak mengarah ke objek apa pun. SystemExit Dibesarkan oleh fungsi sys.exit (). StandardError Kelas dasar untuk semua pengecualian built-in kecuali StopIteration dan SystemExit. ArithmeticError Kelas dasar untuk semua kesalahan yang terjadi untuk perhitungan numerik. OverflowError Dibesarkan saat perhitungan melebihi batas maksimum untuk tipe numerik. FloatingPointError Dibesarkan saat perhitungan floating point gagal. ZeroDivisonError Dibesarkan saat pembagian atau modulo nol dilakukan untuk semua tipe numerik. AssertionError Dibesarkan jika terjadi kegagalan pernyataan Assert. AttributeError Dibesarkan jika terjadi kegagalan referensi atribut atau penugasan. StopIteration0 Dibesarkan bila tidak ada input dari fungsi raw_input () atau input () dan akhir file tercapai. StopIteration1 Dibesarkan saat sebuah pernyataan impor gagal. StopIteration2 Dibesarkan saat pengguna menyela eksekusi program, biasanya dengan menekan Ctrl + c. StopIteration3 Kelas dasar untuk semua kesalahan pencarian. StopIteration4 Dibesarkan saat sebuah indeks tidak ditemukan secara berurutan. StopIteration5 Dibesarkan saat kunci yang ditentukan tidak ditemukan dalam kamus. StopIteration6 Dibesarkan saat pengenal tidak ditemukan di namespace lokal atau global. StopIteration7 Dibesarkan saat mencoba mengakses variabel lokal dalam suatu fungsi atau metode namun tidak ada nilai yang ditugaskan padanya. StopIteration8 Kelas dasar untuk semua pengecualian yang terjadi di luar lingkungan Python. StopIteration9 Dibesarkan saat operasi input / output gagal, seperti pernyataan cetak atau fungsi open () saat mencoba membuka file yang tidak ada. SystemExit0 Dibangkitkan untuk kesalahan terkait sistem operasi. SystemExit1 Dibesarkan saat ada kesalahan dengan sintaks Python. SystemExit2 Dibesarkan saat indentasi tidak ditentukan dengan benar. SystemExit3 Dibesarkan saat penafsir menemukan masalah internal, namun bila kesalahan ini ditemui juru bahasa Python tidak keluar. SystemExit Dibesarkan saat juru bahasa Python berhenti dengan menggunakan fungsi sys.exit (). Jika tidak ditangani dalam kode, menyebabkan penafsir untuk keluar. SystemExit5 Dibesarkan saat operasi atau fungsi dicoba yang tidak valid untuk tipe data yang ditentukan. SystemExit6 Dibesarkan ketika fungsi bawaan untuk tipe data memiliki jenis argumen yang valid, namun argumen tersebut memiliki nilai yang tidak valid yang ditentukan. SystemExit7 Dibesarkan saat kesalahan yang dihasilkan tidak termasuk dalam kategori apa pun. SystemExit8 Dibesarkan ketika metode abstrak yang perlu diimplementasikan di kelas warisan sebenarnya tidak dilaksanakan.

---

Raise an exception

As a Python developer you can choose to throw an exception if a condition occurs.

To throw (or raise) an exception, use the raise keyword.

Example

Raise an error and stop the program if x is lower than 0:

x = -1

if x < 0:
  raise Exception("Sorry, no numbers below zero")

Try it Yourself »

The raise keyword is used to raise an exception.

You can define what kind of error to raise, and the text to print to the user.

Example

Raise a TypeError if x is not an integer:

x = "hello"

if not type(x) is int:
  raise TypeError("Only integers are allowed")

Try it Yourself »

---

---

Avoid raising a generic

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

0. To catch it, you'll have to catch all other more specific exceptions that subclass it.

Problem 1: Hiding bugs

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

For example:

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

Problem 2: Won't catch

And more specific catches won't catch the general exception:

def demo_no_catch():
    try:
        raise Exception('general exceptions not caught by specific handling')
    except ValueError as e:
        print('we will not catch exception: Exception')
 

>>> demo_no_catch()
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 3, in demo_no_catch
Exception: general exceptions not caught by specific handling

Best Practices: def demo_bad_catch(): try: raise ValueError('Represents a hidden bug, do not catch this') raise Exception('This is the exception you expect to handle') except Exception as error: print('Caught this error: ' + repr(error)) >>> demo_bad_catch() Caught this error: ValueError('Represents a hidden bug, do not catch this',) 1 statement

.

raise ValueError('A very specific bad thing happened')

which also handily allows an arbitrary number of arguments to be passed to the constructor:

raise ValueError('A very specific bad thing happened', 'foo', 'bar', 'baz') 

These arguments are accessed by the

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

2 attribute on the

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

0 object. For example:

try:
    some_code_that_may_raise_our_value_error()
except ValueError as err:
    print(err.args)

prints

('message', 'foo', 'bar', 'baz')    

In Python 2.5, an actual

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

4 attribute was added to

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

5 in favor of encouraging users to subclass Exceptions and stop using

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

2, but .

Best Practices: def demo_bad_catch(): try: raise ValueError('Represents a hidden bug, do not catch this') raise Exception('This is the exception you expect to handle') except Exception as error: print('Caught this error: ' + repr(error)) >>> demo_bad_catch() Caught this error: ValueError('Represents a hidden bug, do not catch this',) 8 clause

When inside an except clause, you might want to, for example, log that a specific type of error happened, and then re-raise. The best way to do this while preserving the stack trace is to use a bare raise statement. For example:

logger = logging.getLogger(__name__)

try:
    do_something_in_app_that_breaks_easily()
except AppError as error:
    logger.error(error)
    raise                 # just this!
    # raise AppError      # Don't do this, you'll lose the stack trace!

Don't modify your errors... but if you insist.

You can preserve the stacktrace (and error value) with

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

9, but this is way more error prone and has compatibility problems between Python 2 and 3, prefer to use a bare

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

1 to re-raise.

To explain - the

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

9 returns the type, value, and traceback.

type, value, traceback = sys.exc_info()

This is the syntax in Python 2 - note this is not compatible with Python 3:

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

0

If you want to, you can modify what happens with your new raise - e.g. setting new

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

2 for the instance:

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

1

And we have preserved the whole traceback while modifying the args. Note that this is not a best practice and it is invalid syntax in Python 3 (making keeping compatibility much harder to work around).

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

2

In :

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

3

Again: avoid manually manipulating tracebacks. It's and more error prone. And if you're using threading and

def demo_no_catch():
    try:
        raise Exception('general exceptions not caught by specific handling')
    except ValueError as e:
        print('we will not catch exception: Exception')
 

>>> demo_no_catch()
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 3, in demo_no_catch
Exception: general exceptions not caught by specific handling

3 you may even get the wrong traceback (especially if you're using exception handling for control flow - which I'd personally tend to avoid.)

Python 3, Exception chaining

In Python 3, you can chain Exceptions, which preserve tracebacks:

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

4

Be aware:

• this does allow changing the error type raised, and
• this is not compatible with Python 2.

Deprecated Methods:

These can easily hide and even get into production code. You want to raise an exception, and doing them will raise an exception, but not the one intended!

Valid in Python 2, but not in Python 3 is the following:

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

5

Only (2.4 and lower), you may still see people raising strings:

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

6

In all modern versions, this will actually raise a

def demo_no_catch():
    try:
        raise Exception('general exceptions not caught by specific handling')
    except ValueError as e:
        print('we will not catch exception: Exception')
 

>>> demo_no_catch()
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 3, in demo_no_catch
Exception: general exceptions not caught by specific handling

4, because you're not raising a

def demo_bad_catch():
    try:
        raise ValueError('Represents a hidden bug, do not catch this')
        raise Exception('This is the exception you expect to handle')
    except Exception as error:
        print('Caught this error: ' + repr(error))

>>> demo_bad_catch()
Caught this error: ValueError('Represents a hidden bug, do not catch this',)

5 type. If you're not checking for the right exception and don't have a reviewer that's aware of the issue, it could get into production.

Example Usage

I raise Exceptions to warn consumers of my API if they're using it incorrectly:

raise Exception('I know Python!') # Don't! If you catch, likely to hide bugs.

7

Create your own error types when apropos

"I want to make an error on purpose, so that it would go into the except"

You can create your own error types, if you want to indicate something specific is wrong with your application, just subclass the appropriate point in the exception hierarchy: