我如何找到執行任務 X 的模組或應用程式？¶

Checkthe Library Reference to see if there's a relevantstandard library module. (Eventually you'll learn what's in the standardlibrary and will be able to skip this step.)

For third-party packages, search thePython Package Index or tryGoogle oranother web search engine. Searching for "Python" plus a keyword or two foryour topic of interest will usually find something helpful.

哪裡可以找到 math.py (socket.py, regex.py, 等...) 來源檔案？¶

If you can't find a source file for a module it may be a built-in ordynamically loaded module implemented in C, C++ or other compiled language.In this case you may not have the source file or it may be something likemathmodule.c, somewhere in a C source directory (not on the Python Path).

有（至少）三種 Python 模組：

1. 以 Python 編寫的模組 (.py)；

2. 用 C 編寫並動態載入的模組（.dll、.pyd、.so、.sl 等）；

3. 用 C 編寫並與直譯器鏈接的模組；要獲得這些 list，請輸入：

   importsysprint(sys.builtin_module_names)

我如何使 Python script 執行在 Unix？¶

You need to do two things: the script file's mode must be executable and thefirst line must begin with#! followed by the path of the Pythoninterpreter.

第一個是透過執行chmod+xscriptfile 或者可能是chmod755scriptfile 來完成的。

第二個則可以透過多種方式完成。最直接的方法是寫：

#!/usr/local/bin/python

as the very first line of your file, using the pathname for where the Pythoninterpreter is installed on your platform.

If you would like the script to be independent of where the Python interpreterlives, you can use theenv program. Almost all Unix variants supportthe following, assuming the Python interpreter is in a directory on the user'sPATH:

#!/usr/bin/env python

不要對 CGI 腳本執行此操作。CGI 腳本的PATH 變數通常非常小，因此你需要使用直譯器的實際絕對路徑名稱。

Occasionally, a user's environment is so full that the/usr/bin/envprogram fails; or there's no env program at all. In that case, you can try thefollowing hack (due to Alex Rezinsky):

#! /bin/sh""":"execpython$0${1+"$@"}"""

次要缺點是這定義了腳本的 __doc__ 字串。但是你可以透過新增下面這一行來解決這個問題：

__doc__="""...Whatever..."""

是否有適用於 Python 的 curses/termcap 套件？¶

For Unix variants: The standard Python source distribution comes with a cursesmodule in theModules subdirectory, though it's not compiled by default.(Note that this is not available in the Windows distribution -- there is nocurses module for Windows.)

Thecurses module supports basic curses features as well as many additionalfunctions from ncurses and SYSV curses such as colour, alternative character setsupport, pads, and mouse support. This means the module isn't compatible withoperating systems that only have BSD curses, but there don't seem to be anycurrently maintained OSes that fall into this category.

Python 中是否有等同於 C 的 onexit() 的函式？¶

Theatexit module provides a register function that is similar to C'sonexit().

為什麼我的訊號處理程式不起作用？¶

The most common problem is that the signal handler is declared with the wrongargument list. It is called as

handler(signum,frame)

所以它應該用兩個參數聲明：

defhandler(signum,frame):...

如何測試 Python 程式或元件？¶

Python comes with two testing frameworks. Thedoctest module findsexamples in the docstrings for a module and runs them, comparing the output withthe expected output given in the docstring.

Theunittest module is a fancier testing framework modelled on Java andSmalltalk testing frameworks.

To make testing easier, you should use good modular design in your program.Your program should have almost all functionalityencapsulated in either functions or class methods -- and this sometimes has thesurprising and delightful effect of making the program run faster (because localvariable accesses are faster than global accesses). Furthermore the programshould avoid depending on mutating global variables, since this makes testingmuch more difficult to do.

The "global main logic" of your program may be as simple as

if__name__=="__main__":main_logic()

at the bottom of the main module of your program.

Once your program is organized as a tractable collection of function and classbehaviours, you should write test functions that exercise the behaviours. Atest suite that automates a sequence of tests can be associated with each module.This sounds like a lot of work, but since Python is so terse and flexible it'ssurprisingly easy. You can make coding much more pleasant and fun by writingyour test functions in parallel with the "production code", since this makes iteasy to find bugs and even design flaws earlier.

"Support modules" that are not intended to be the main module of a program mayinclude a self-test of the module.

if__name__=="__main__":self_test()

Even programs that interact with complex external interfaces may be tested whenthe external interfaces are unavailable by using "fake" interfaces implementedin Python.

如何從文件字串建立文件？¶

Thepydoc module can create HTML from the doc strings in your Pythonsource code. An alternative for creating API documentation purely fromdocstrings isepydoc.Sphinx can also include docstring content.

How do I get a single keypress at a time?¶

For Unix variants there are several solutions. It's straightforward to do thisusing curses, but curses is a fairly large module to learn.

如何使用執行緒編寫程式？¶

Be sure to use thethreading module and not the_thread module.Thethreading module builds convenient abstractions on top of thelow-level primitives provided by the_thread module.

我的執行緒似乎都沒有運行：為什麼？¶

As soon as the main thread exits, all threads are killed. Your main thread isrunning too quickly, giving the threads no time to do any work.

A simple fix is to add a sleep to the end of the program that's long enough forall the threads to finish:

importthreading,timedefthread_task(name,n):foriinrange(n):print(name,i)foriinrange(10):T=threading.Thread(target=thread_task,args=(str(i),i))T.start()time.sleep(10)# <---------------------------!

But now (on many platforms) the threads don't run in parallel, but appear to runsequentially, one at a time! The reason is that the OS thread scheduler doesn'tstart a new thread until the previous thread is blocked.

A simple fix is to add a tiny sleep to the start of the run function:

defthread_task(name,n):time.sleep(0.001)# <--------------------!foriinrange(n):print(name,i)foriinrange(10):T=threading.Thread(target=thread_task,args=(str(i),i))T.start()time.sleep(10)

Instead of trying to guess a good delay value fortime.sleep(),it's better to use some kind of semaphore mechanism. One idea is to use thequeue module to create a queue object, let each thread append a token tothe queue when it finishes, and let the main thread read as many tokens from thequeue as there are threads.

How do I parcel out work among a bunch of worker threads?¶

The easiest way is to use theconcurrent.futures module,especially theThreadPoolExecutor class.

Or, if you want fine control over the dispatching algorithm, you can writeyour own logic manually. Use thequeue module to create a queuecontaining a list of jobs. TheQueue class maintains alist of objects and has a.put(obj) method that adds items to the queue anda.get() method to return them. The class will take care of the lockingnecessary to ensure that each job is handed out exactly once.

這是一個簡單的例子：

importthreading,queue,time# The worker thread gets jobs off the queue.  When the queue is empty, it# assumes there will be no more work and exits.# (Realistically workers will run until terminated.)defworker():print('Running worker')time.sleep(0.1)whileTrue:try:arg=q.get(block=False)exceptqueue.Empty:print('Worker',threading.current_thread(),end=' ')print('queue empty')breakelse:print('Worker',threading.current_thread(),end=' ')print('running with argument',arg)time.sleep(0.5)# Create queueq=queue.Queue()# Start a pool of 5 workersforiinrange(5):t=threading.Thread(target=worker,name='worker%i'%(i+1))t.start()# Begin adding work to the queueforiinrange(50):q.put(i)# Give threads time to runprint('Main thread sleeping')time.sleep(5)

運行時，這將產生以下輸出：

Running workerRunning workerRunning workerRunning workerRunning workerMain thread sleepingWorker <Thread(worker 1, started 130283832797456)> running with argument 0Worker <Thread(worker 2, started 130283824404752)> running with argument 1Worker <Thread(worker 3, started 130283816012048)> running with argument 2Worker <Thread(worker 4, started 130283807619344)> running with argument 3Worker <Thread(worker 5, started 130283799226640)> running with argument 4Worker <Thread(worker 1, started 130283832797456)> running with argument 5...

Consult the module's documentation for more details; theQueueclass provides a featureful interface.

What kinds of global value mutation are thread-safe?¶

Aglobal interpreter lock (GIL) is used internally to ensure that only onethread runs in the Python VM at a time. In general, Python offers to switchamong threads only between bytecode instructions; how frequently it switches canbe set viasys.setswitchinterval(). Each bytecode instruction andtherefore all the C implementation code reached from each instruction istherefore atomic from the point of view of a Python program.

In theory, this means an exact accounting requires an exact understanding of thePVM bytecode implementation. In practice, it means that operations on sharedvariables of built-in data types (ints, lists, dicts, etc) that "look atomic"really are.

For example, the following operations are all atomic (L, L1, L2 are lists, D,D1, D2 are dicts, x, y are objects, i, j are ints):

L.append(x)L1.extend(L2)x=L[i]x=L.pop()L1[i:j]=L2L.sort()x=yx.field=yD[x]=yD1.update(D2)D.keys()

這些不是：

i=i+1L.append(L[-1])L[i]=L[j]D[x]=D[x]+1

Operations that replace other objects may invoke those other objects'__del__() method when their reference count reaches zero, and that canaffect things. This is especially true for the mass updates to dictionaries andlists. When in doubt, use a mutex!

不能擺脫全域直譯器鎖嗎？¶

Theglobal interpreter lock (GIL) is often seen as a hindrance to Python'sdeployment on high-end multiprocessor server machines, because a multi-threadedPython program effectively only uses one CPU, due to the insistence that(almost) all Python code can only run while the GIL is held.

With the approval ofPEP 703 work is now underway to remove the GIL from theCPython implementation of Python. Initially it will be implemented as anoptional compiler flag when building the interpreter, and so separatebuilds will be available with and without the GIL. Long-term, the hope isto settle on a single build, once the performance implications of removing theGIL are fully understood. Python 3.13 is likely to be the first releasecontaining this work, although it may not be completely functional in thisrelease.

The current work to remove the GIL is based on afork of Python 3.9 with the GIL removedby Sam Gross.Prior to that,in the days of Python 1.5, Greg Stein actually implemented a comprehensivepatch set (the "free threading" patches) that removed the GIL and replaced itwith fine-grained locking. Adam Olsen did a similar experimentin hispython-safethreadproject. Unfortunately, both of these earlier experiments exhibited a sharpdrop in single-threadperformance (at least 30% slower), due to the amount of fine-grained lockingnecessary to compensate for the removal of the GIL. The Python 3.9 forkis the first attempt at removing the GIL with an acceptable performanceimpact.

The presence of the GIL in current Python releasesdoesn't mean that you can't make good use of Python on multi-CPU machines!You just have to be creative with dividing the work up between multipleprocesses rather than multiplethreads. TheProcessPoolExecutor class in the newconcurrent.futures module provides an easy way of doing so; themultiprocessing module provides a lower-level API in case you wantmore control over dispatching of tasks.

Judicious use of C extensions will also help; if you use a C extension toperform a time-consuming task, the extension can release the GIL while thethread of execution is in the C code and allow other threads to get some workdone. Some standard library modules such aszlib andhashlibalready do this.

減少 GIL 影響的另一種方法是將 GIL 設置為直譯器各自狀態的鎖 (per-interpreter-state lock)，而不是真正的全域鎖。這在Python 3.12 中首次實現，並且可於 C API 中使用。預計 Python 3.13 將會提供其 Python 介面。目前主要的限制可能是第三方擴充模組，因為實作時必須考慮到多個直譯器才能使用，因此許多舊的擴充模組將無法使用。

如何刪除檔案？（以及其他檔案問題...）¶

Useos.remove(filename) oros.unlink(filename); for documentation, seetheos module. The two functions are identical;unlink() is simplythe name of the Unix system call for this function.

To remove a directory, useos.rmdir(); useos.mkdir() to create one.os.makedirs(path) will create any intermediate directories inpath thatdon't exist.os.removedirs(path) will remove intermediate directories aslong as they're empty; if you want to delete an entire directory tree and itscontents, useshutil.rmtree().

要重新命名檔案，請使用os.rename(old_path,new_path)。

To truncate a file, open it usingf=open(filename,"rb+"), and usef.truncate(offset); offset defaults to the current seek position. There'salsoos.ftruncate(fd,offset) for files opened withos.open(), wherefd is the file descriptor (a small integer).

Theshutil module also contains a number of functions to work on filesincludingcopyfile(),copytree(), andrmtree().

如何複製檔案？¶

Theshutil module contains acopyfile() function.Note that on Windows NTFS volumes, it does not copyalternate data streamsnorresource forkson macOS HFS+ volumes, though both are now rarely used.It also doesn't copy file permissions and metadata, though usingshutil.copy2() instead will preserve most (though not all) of it.

如何讀取（或寫入）二進位制資料？¶

To read or write complex binary data formats, it's best to use thestructmodule. It allows you to take a string containing binary data (usually numbers)and convert it to Python objects; and vice versa.

For example, the following code reads two 2-byte integers and one 4-byte integerin big-endian format from a file:

importstructwithopen(filename,"rb")asf:s=f.read(8)x,y,z=struct.unpack(">hhl",s)

The '>' in the format string forces big-endian data; the letter 'h' reads one"short integer" (2 bytes), and 'l' reads one "long integer" (4 bytes) from thestring.

For data that is more regular (e.g. a homogeneous list of ints or floats),you can also use thearray module.

我似乎無法在用 os.popen() 建立的 pipe 上使用 os.read()；為什麼？¶

os.read() is a low-level function which takes a file descriptor, a smallinteger representing the opened file.os.popen() creates a high-levelfile object, the same type returned by the built-inopen() function.Thus, to readn bytes from a pipep created withos.popen(), you need tousep.read(n).

如何存取序列 (RS232) 連接埠？¶

對於 Win32、OSX、Linux、BSD、Jython、IronPython：

pyserial

對於 Unix，請參閱 Mitch Chapman 的 Usenet 貼文：

https://groups.google.com/groups?selm=34A04430.CF9@ohioee.com

為什麼關閉 sys.stdout (stdin, stderr) 並沒有真正關閉它？¶

Python檔案物件是低階 C 檔案描述器的高階抽象層。

For most file objects you create in Python via the built-inopen()function,f.close() marks the Python file object as being closed fromPython's point of view, and also arranges to close the underlying C filedescriptor. This also happens automatically inf's destructor, whenf becomes garbage.

But stdin, stdout and stderr are treated specially by Python, because of thespecial status also given to them by C. Runningsys.stdout.close() marksthe Python-level file object as being closed, but doesnot close theassociated C file descriptor.

To close the underlying C file descriptor for one of these three, you shouldfirst be sure that's what you really want to do (e.g., you may confuseextension modules trying to do I/O). If it is, useos.close():

os.close(stdin.fileno())os.close(stdout.fileno())os.close(stderr.fileno())

或者你可以分別使用數字常數 0、1 和 2。

Python 有哪些 WWW 工具？¶

See the chapters titled網路協定 (Internet protocols) 及支援 and網際網路資料處理 in the LibraryReference Manual. Python has many modules that will help you build server-sideand client-side web systems.

A summary of available frameworks is maintained by Paul Boddie athttps://wiki.python.org/moin/WebProgramming.

我應該使用什麼模組來輔助產生 HTML？¶

You can find a collection of useful links on theWeb Programming wiki page.

如何從 Python 腳本發送郵件？¶

使用標準函式庫模組smtplib。

Here's a very simple interactive mail sender that uses it. This method willwork on any host that supports an SMTP listener.

importsys,smtplibfromaddr=input("From: ")toaddrs=input("To: ").split(',')print("Enter message, end with ^D:")msg=''whileTrue:line=sys.stdin.readline()ifnotline:breakmsg+=line# The actual mail sendserver=smtplib.SMTP('localhost')server.sendmail(fromaddr,toaddrs,msg)server.quit()

A Unix-only alternative uses sendmail. The location of the sendmail programvaries between systems; sometimes it is/usr/lib/sendmail, sometimes/usr/sbin/sendmail. The sendmail manual page will help you out. Here'ssome sample code:

importosSENDMAIL="/usr/sbin/sendmail"# sendmail locationp=os.popen("%s -t -i"%SENDMAIL,"w")p.write("To: receiver@example.com\n")p.write("Subject: test\n")p.write("\n")# blank line separating headers from bodyp.write("Some text\n")p.write("some more text\n")sts=p.close()ifsts!=0:print("Sendmail exit status",sts)

How do I avoid blocking in the connect() method of a socket?¶

select 模組通常用於幫助處理 socket 上的非同步 I/O。

To prevent the TCP connect from blocking, you can set the socket to non-blockingmode. Then when you do theconnect(),you will either connect immediately(unlikely) or get an exception that contains the error number as.errno.errno.EINPROGRESS indicates that the connection is in progress, but hasn'tfinished yet. Different OSes will return different values, so you're going tohave to check what's returned on your system.

You can use theconnect_ex() methodto avoid creating an exception.It will just return the errno value.To poll, you can callconnect_ex() again later--0 orerrno.EISCONN indicate that you're connected -- or you can pass thissocket toselect.select() to check if it's writable.

Python 中是否有任何資料庫套件的介面？¶

有的。

Interfaces to disk-based hashes such asDBM andGDBM are also included with standard Python. There is also thesqlite3 module, which provides a lightweight disk-based relationaldatabase.

Support for most relational databases is available. See theDatabaseProgramming wiki page for details.

你如何在 Python 中實作持久性物件？¶

Thepickle library module solves this in a very general way (though youstill can't store things like open files, sockets or windows), and theshelve library module uses pickle and (g)dbm to create persistentmappings containing arbitrary Python objects.

如何在 Python 中生成隨機數？¶

標準模組random 實作了一個隨機數生成器。用法很簡單：

importrandomrandom.random()

這將回傳 [0, 1) 範圍內的隨機浮點數。

該模組中還有許多其他專用生成器，例如：

• randrange(a,b) 會選擇 [a, b) 範圍內的一個整數。

• uniform(a,b) 會選擇 [a, b) 範圍內的浮點數。

• normalvariate(mean,sdev) 對常態（高斯）分佈進行取樣 (sample)。

一些更高階的函式會直接對序列進行操作，例如：

• choice(S) 會從給定序列中選擇一個隨機元素。

• shuffle(L) 會原地 (in-place) 打亂 list，即隨機排列它。

還有一個Random 類別，你可以將它實例化以建立多個獨立的隨機數生成器。