o_18ufhmfmq19t513t3lgmn5l1qa8a.pdf

568 APPENDIX B ■ PYTHON REFERENCE
The raise Statement
The raise statement raises an exception. It may be used without any arguments (inside an
except clause, to re-raise the currently caught exception), with a subclass of Exception and an
optional argument (in which case an instance is constructed), or with an instance of a subclass
of Exception.
Examples:
raise
# May only be used inside except clauses
raise IndexError
raise IndexError, 'index out of bounds'
raise IndexError('index out of bounds')
The break Statement
The break statement ends the immediately enclosing loop statement (for or while) and continues
execution immediately after that loop statement.
Example:
while True:
line = file.readline()
if not line: break
print line
The continue Statement
The continue statement is similar to the break statement in that it halts the current iteration of
the immediately enclosing loop, but instead of ending the loop completely, it continues execution
at the beginning of the next iteration.
Example:
while True:
line = file.readline()
if not line: break
if line.isspace(): continue
print line
The import Statement
The import statement is used to import names (variables bound to functions, classes, or other
values) from an external module.
Examples:
import math
from math import sqrt
from math import sqrt as squareroot
from math import *