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jython学习笔记3
1.os.environ["HOME"] 为什么这句话在我的STS中打印不出东西，还报错
| Method | Description |
| close() | Close file |
| fileno() | Returns integer file descriptor |
| flush() | Used to flush or clear the output buffers and write content to the file |
| isatty() | If the file is an interactive terminal, returns 1 |
| next() | This allows the file to be iterated over. Returns the next line in the file. If no line is found, raises StopIteration |
| read(x) | Reads x bytes |
| readline(x) | Reads single line up to x characters, or entire line if x is omitted |
| readlines(size) | Reads all lines in file into a list. If size > 0, reads that number of characters |
| seek() | Moves cursor to a new position in the file |
| tell() | Returns the current position of the cursor |
| truncate(size) | Truncates file’s size. Size defaults to current position unless specified |
| write(string) | Writes a string to the file object |
| writelines(seq) | Writes all strings contained in a sequence with no separator |
| Attribute | Description |
| closed | Returns a boolean to indicate if the file is closed |
| encoding | Returns a string indicating encoding on file |
| mode | Returns the I/O mode for a file(i.e., ‘r’, ‘w’, ‘r+,’rb’, etc.) |
| name | Returns the name of the file |
| newlines | Returns the newline representation in the file. This keeps track of the types of newlines encountered while reading the file. Allows for universal newline support. |
在定义类时，Car(object)，指定义的是object的一个子类。类的属性可以不用实例化而直接用。self的变量只能用在单一的object中，而类的属性则属于该类的所有实例，也就是说，改变类的可改变变量（例如LIST）会影响到该类的所有实例，改变类的某一个实例中该类的不可改变属性，例如integer，本实例中的该类属性的值改变，其他实例中该类的属性的值不变。
2.jython使用left first depth first
3.这段代码感觉看不懂
from __future__ import with_statement
from contextlib import closing
from pickle import dumps, loads
def write_object(fout, obj):
data = dumps(obj)
fout.write("%020d" % len(data))
fout.write(data)
def read_object(fin):
length = int(fin.read(20))
obj = loads(fin.read(length))
return obj
class Simple(object):
def __init__(self, value):
self.value = value
def __unicode__(self):
return "Simple[%s]" % self.value
with closing(open(‘simplefile‘,‘wb‘)) as fout:
for i in range(10):
obj = Simple(i)
write_object(fout, obj)
print "Loading objects from disk!"
print ‘=‘ * 20
with closing(open(‘simplefile‘,‘rb‘)) as fin:
for i in range(10):
print read_object(fin)
3.chapter6看得有点不太懂。先跳过，等回过头再看一遍
Table 7-1. Exceptions
| Exception | Description |
| BaseException | This is the root exception for all others |
| GeneratorExit | Raised by close() method of generators for terminating iteration |
| KeyboardInterrupt | Raised by the interrupt key |
| SystemExit | Program exit |
| Exception | Root for all non-exiting exceptions |
| StopIteration | Raised to stop an iteration action |
| StandardError | Base class for all built-in exceptions |
| ArithmeticError | Base for all arithmetic exceptions |
| FloatingPointError | Raised when a floating-point operation fails |
| OverflowError | Arithmetic operations that are too large |
| ZeroDivisionError | Division or modulo operation with zero as divisor |
| AssertionError | Raised when an assert statement fails |
| AttributeError | Attribute reference or assignment failure |
| EnvironmentError | An error occurred outside of Python |
| IOError | Error in Input/Output operation |
| OSError | An error occurred in the os module |
| EOFError | input() or raw_input() tried to read past the end of a file |
| ImportError | Import failed to find module or name |
| LookupError | Base class for IndexError and KeyError |
| IndexError | A sequence index goes out of range |
| KeyError | Referenced a non-existent mapping (dict) key |
| MemoryError | Memory exhausted |
| NameError | Failure to find a local or global name |
| UnboundLocalError | Unassigned local variable is referenced |
| ReferenceError | Attempt to access a garbage-collected object |
| RuntimeError | Obsolete catch-all error |
| NotImplementedError | Raised when a feature is not implemented |
| SyntaxError | Parser encountered a syntax error |
| IndentationError | Parser encountered an indentation issue |
| TabError | Incorrect mixture of tabs and spaces |
| SystemError | Non-fatal interpreter error |
| TypeError | Inappropriate type was passed to an operator or function |
| ValueError | Argument error not covered by TypeError or a more precise error |
| Warning | Base for all warnings |
4.
Table 7-2. Python Warning Categories
| Warning | Description |
| Warning | Root warning class |
| UserWarning | A user-defined warning |
| DeprecationWarning | Warns about use of a deprecated feature |
| SyntaxWarning | Syntax issues |
| RuntimeWarning | Runtime issues |
| FutureWarning | Warns that a particular feature will be changing in a future release |
Importing the warnings module into your code gives you access to a number of built-in warning functions that can be used. If you’d like to filter a warning and change its behavior then you can do so by creating a filter. Table 7-3 lists functions that come with the warnings module.
Table 7-3. Warning Functions
| Function | Description |
| warn(message[, category[, stacklevel]]) | Issues a warning. Parameters include a message string, the optional category of warning, and the optional stack level that tells which stack frame the warning should originate from, usually either the calling function or the source of the function itself. |
| warn_explicit(message, category, filename, lineno[, module[, registry]]) | This offers a more detailed warning message and makes category a mandatory parameter. filename, lineno, and module tell where the warning is located. registry represents all of the current warning filters that are active. |
| showwarning(message, category, filename, lineno[, file]) | Gives you the ability to write the warning to a file. |
| formatwarning(message, category, filename, lineno) | Creates a formatted string representing the warning. |
| simplefilter(action[, category[, lineno[, append]]]) | Inserts simple entry into the ordered list of warnings filters. Regular expressions are not needed for simplefilter as the filter always matches any message in any module as long as the category and line number match. filterwarnings() described below uses a regular expression to match against warnings. |
| resetwarnings() | Resets all of the warning filters. |
| filterwarnings(action[, message[, category[, module[, lineno[, append]]]]]) | This adds an entry into a warning filter list. Warning filters allow you to modify the behavior of a warning. The action in the warning filter can be one from those listed in Table 7-4, message is a regular expression, category is the type of a warning to be issued, module can be a regular expression, lineno is a line number to match against all lines, append specifies whether the filter should be appended to the list of all filters. |
Table 7-4. Python Filter Actions
| Filter Actions | |
| ‘always’ | Always print warning message |
| ‘default’ | Print warning once for each location where warning occurs |
| ‘error’ | Converts a warning into an exception |
| ‘ignore’ | Ignores the warning |
| ‘module’ | Print warning once for each module in which warning occurs |
| ‘once’ | Print warning only one time |
jython学习笔记3