Python 解释器通常安装于
/usr/local/bin/python3.9
在那些可用机器中；放置
/usr/local/bin
在 Unix Shell 搜索路径中，通过键入命令来启动它是可能的：
python3.9
to the shell.
1
Since the choice of the directory where the interpreter lives is an installation option, other places are possible; check with your local Python guru or system administrator. (E.g.,
/usr/local/python
is a popular alternative location.)
On Windows machines where you have installed Python from the
Microsoft Store
，
python3.9
command will be available. If you have the
py.exe 启动器
installed, you can use the
py
command. See
Excursus: Setting environment variables
for other ways to launch Python.
Typing an end-of-file character (
Control-D
在 Unix，
Control-Z
on Windows) at the primary prompt causes the interpreter to exit with a zero exit status. If that doesn’t work, you can exit the interpreter by typing the following command:
quit()
.
The interpreter’s line-editing features include interactive editing, history substitution and code completion on systems that support the
GNU Readline
library. Perhaps the quickest check to see whether command line editing is supported is typing
Control-P
to the first Python prompt you get. If it beeps, you have command line editing; see Appendix
交互输入编辑和历史代入
for an introduction to the keys. If nothing appears to happen, or if
^P
is echoed, command line editing isn’t available; you’ll only be able to use backspace to remove characters from the current line.
The interpreter operates somewhat like the Unix shell: when called with standard input connected to a tty device, it reads and executes commands interactively; when called with a file name argument or with a file as standard input, it reads and executes a script from that file.
A second way of starting the interpreter is
python -c command [arg] ...
, which executes the statement(s) in
command
, analogous to the shell’s
-c
option. Since Python statements often contain spaces or other characters that are special to the shell, it is usually advised to quote
command
in its entirety with single quotes.
Some Python modules are also useful as scripts. These can be invoked using
python -m module [arg] ...
, which executes the source file for
模块
as if you had spelled out its full name on the command line.
When a script file is used, it is sometimes useful to be able to run the script and enter interactive mode afterwards. This can be done by passing
-i
在脚本之前。
所有命令行选项的描述在 命令行和环境 .
When known to the interpreter, the script name and additional arguments thereafter are turned into a list of strings and assigned to the
argv
variable in the
sys
module. You can access this list by executing
import
sys
. The length of the list is at least one; when no script and no arguments are given,
sys.argv[0]
is an empty string. When the script name is given as
'-'
(meaning standard input),
sys.argv[0]
被设为
'-'
。当
-c
command
被使用，
sys.argv[0]
被设为
'-c'
。当
-m
模块
被使用，
sys.argv[0]
is set to the full name of the located module. Options found after
-c
command
or
-m
模块
are not consumed by the Python interpreter’s option processing but left in
sys.argv
for the command or module to handle.
When commands are read from a tty, the interpreter is said to be in
交互模式
. In this mode it prompts for the next command with the
primary prompt
, usually three greater-than signs (
>>>
); for continuation lines it prompts with the
secondary prompt
, by default three dots (
...
). The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt:
$ python3.9
Python 3.9 (default, June 4 2019, 09:25:04)
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
Continuation lines are needed when entering a multi-line construct. As an example, take a look at this
if
语句：
>>> the_world_is_flat = True
>>> if the_world_is_flat:
... print("Be careful not to fall off!")
...
Be careful not to fall off!
有关交互模式的更多信息，见 交互模式 .
By default, Python source files are treated as encoded in UTF-8. In that encoding, characters of most languages in the world can be used simultaneously in string literals, identifiers and comments — although the standard library only uses ASCII characters for identifiers, a convention that any portable code should follow. To display all these characters properly, your editor must recognize that the file is UTF-8, and it must use a font that supports all the characters in the file.
To declare an encoding other than the default one, a special comment line should be added as the first line of the file. The syntax is as follows:
# -*- coding: encoding -*-
where
encoding
is one of the valid
codecs
supported by Python.
For example, to declare that Windows-1252 encoding is to be used, the first line of your source code file should be:
# -*- coding: cp1252 -*-
One exception to the first line rule is when the source code starts with a UNIX “shebang” line . In this case, the encoding declaration should be added as the second line of the file. For example:
#!/usr/bin/env python3
# -*- coding: cp1252 -*-
脚注
On Unix, the Python 3.x interpreter is by default not installed with the executable named
python
, so that it does not conflict with a simultaneously installed Python 2.x executable.