def add_hello():
exec "def hello(): print 'hello'"
hello()
add_hello() # "hello"
hello() # NameError: name 'hello' is not defined
def add_hello():
exec "def hello(): print 'hello'" in locals(), globals()
hello()
add_hello() # "hello"
hello() # "hello"
$ ltrace getent hosts 127.0.0.1 2>&1 | grep gethostby
gethostbyaddr("\177", 4, 2) = 0xb7ed0aa0
$ strace getent hosts 127.0.0.1 2>&1 | grep "/etc/hosts"
open("/etc/hosts", O_RDONLY|O_CLOEXEC) = 3
$ strace host 127.0.0.1 2>&1 | grep "/etc/hosts"
$ ltrace host 127.0.0.1 2>&1 | grep gethostby#include <stdio.h>
int main(void)
{
printf("hello, world!\n");
puts("hello, world!\n");
printf("hello, world! %d\n", 3);
return 0;
}
$ ltrace ./f > /dev/null __libc_start_main(0x80483f4, 1, 0xbf812ab4, 0x8048450, 0x8048440puts("hello, world!") = 14 puts("hello, world!\n") = 15 printf("hello, world! %d\n", 3) = 16 +++ exited (status 0) +++
$ printf '#include <stdio.h>\n#include <assert.h>\nvoid gethostbyaddr(void) { assert(0); }\n' > t.c
$ gcc -fPIC -shared t.c -o t.so
$ LD_PRELOAD=./t.so getent hosts 127.0.0.1
getent: t.c:3: gethostbyaddr: Assertion `0' failed.
Aborted
$ LD_PRELOAD=./t.so host 127.0.0.1
1.0.0.127.in-addr.arpa domain name pointer localhost.
1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions eg /etc/passwd
6 Games
7 Miscellaneous (including macro packages and conven-
tions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]
2012-01-30 更新
見 tag strace 下的新文章, 了解比較詳細的 strace 使用例子。
sudo aptitude install manpages-dev
1.2.3.4 myhost.org.tw myhost這樣就不會去問 DNS 等個五秒才放棄。
import socket
print socket.gethostbyaddr('127.0.0.1')This is a common problem that newbies run into. Answer: host(1) and nslookup(1) does not call gethostbyname(3) or the IPv6 safe getnameinfo(3) but issue DNS requests directly.
What you want is getent(1) from glibc:
getent hosts 127.0.0.1
(defmacro backwards (expr) (reverse expr))
CL-USER> (backwards ("hello, world" t format))
hello, world
NIL
CL-USER> (macroexpand-1 '(backwards ("hello, world" t format)))
(FORMAT T "hello, world")
Tthe Lisp compiler passes the arguments, unevaluated, to the macro code, which returns a new Lisp expression that is then evaluated in place of the original macro call.
The problem: Write a function foo that takes a number n and returns a function that takes a number i, and returns n incremented by i.該文用 OOP 實作, 程式如下 (摘錄自該文, 並加上 object):
class foo(object):
def __init__(self, n):
self.n = n
def __call__(self, i):
self.n += i
return self.n
def foo(n):
def inc(i):
inc.n += i
return inc.n
inc.n = n
return inc
autocmd BufRead,BufNewFile *.py map <F10> :% w !python
autocmd BufRead,BufNewFile *.py vmap f :w !python
cat MY_SCRIPT.py | python第二行將指令對應到 visual mode (按 V, v, Ctrl+v 選取區塊), 選好區塊後按 f 會執行被選到的那幾行程式。假設選到的是第三到五行, 相當於在 shell 下這麼做:
head -5 MY_SCRIPT.py | tail -3 | python選用 f 只是我個人習慣 (最不費力的鍵), 大家可以換成自己喜歡的鍵。其它語言只要有直譯器, 把設定中的 python 換成該直譯器 (比方 ruby), *.py 換成對應的副檔名 (比方 *.rb) 即可。
filetype plugin on或
autocmd BufRead,BufNewFile *.lisp so ~/.vim/ftplugin/lisp/limp.vim
dpkg-reconfigure tzdata
sudo aptitude install rlwrap啟動方式是:
rlwrap ARGUMENT COMMAND以 sqlite3 為例, 啟動方式是:
rlwrap -a -r sqlite3-a 表示不管原本的程式是否有用 readline, 都改用 rlwrap。 -r 表示記下所有打過和螢幕上出現的字彙。如此一來執行 「select * from my_table;」之後, 可以直接按 tab 補完 column name 或 table name 。
SELECT HOUR(created_time) AS h, FLOOR(MINUTE(created_time) / 30) AS v, COUNT(*) FROM record WHERE AND created_time >= '2010-02-10' AND created_time < FROM_DAYS(TO_DAYS('2010-02-10') + 1) GROUP BY h, v;
a == b # call a.__eq__
a != b # call a.__ne__所以, 有可能發生 a== b 為 True, a != b 也為 True 的奇怪情況。這和 Java 只要 (只能) 覆寫 equals() 不同。
class A(object):
def __eq__(self, other):
# Write your code here
def __ne__(self, other):
return not self == other
debug1: SSH2_MSG_SERVICE_ACCEPT receivedgoogle 後發現這篇提到這可能是 DNS 查不到 IP 的 domain name 造成的, 所以我試了一下:
cobd3=Drives\base_10G.vdi
cobd0=Drives\base_10G.vdi
cobd3=Drives\base.vdi