Built-in Exceptions
This section describes the exceptions that Python may raise during a
program’s execution. Beginning with Python 1.5, all built-in
exceptions are class objects. Prior to 1.5, they were strings. Class
exceptions are mostly indistinguishable from strings, unless they are
concatenated. Built-in exceptions are defined in the module
exceptions
; this module never needs to be imported
explicitly, because the exception names are provided in the built-in
scope namespace. Most built-in exceptions have an associated extra
data value with details.
Base Classes (Categories)
Exception
Root superclass for all exceptions. User-defined exceptions may be derived from this class, but this is not currently enforced or required.
StandardError
Superclass for all other built-in exceptions except for
SystemExit
; subclass of theException
root class.ArithmeticError
Superclass for
OverflowError
,ZeroDivisionError
,FloatingPointError
; subclass ofStandardError
.LookupError
Superclass for
IndexError
,KeyError
; subclass ofStandardError
.EnvironmentError
Superclass for exceptions that occur outside Python (
IOError
,OSError
); subclass ofStandardError
. New in Release 1.5.2.
Specific Exceptions Raised
AssertionError
When an
assert
statement’s test is false.AttributeError
On attribute reference or assignment failure.
EOFError
When immediate end of file is hit by
input( )
orraw_input( )
.FloatingPointError
On floating-point operation failure.
IOError
On I/O or file-related operation failure.
ImportError ...
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