Running Files with Command Lines

Once you’ve saved this text file, you can ask Python to run it by listing its full filename as the first argument to a python command, typed at the system shell prompt:

% python script1.py
win32
1267650600228229401496703205376
Spam!Spam!Spam!Spam!Spam!Spam!Spam!Spam!

广告：个人专属 VPN，独立 IP，无限流量，多机房切换，还可以屏蔽广告和恶意软件，每月最低仅 5 美元

Again, you can type such a system shell command in whatever your system provides for command-line entry—a Windows Command Prompt window, an xterm window, or similar. Remember to replace “python” with a full directory path, as before, if your PATH setting is not configured.

If all works as planned, this shell command makes Python run the code in this file line by line, and you will see the output of the script’s three print statements—the name of the underlying platform, 2 raised to the power 100, and the result of the same string repetition expression we saw earlier (again, more on the last two of these in Chapter 4).

If all didn’t work as planned, you’ll get an error message—make sure you’ve entered the code in your file exactly as shown, and try again. We’ll talk about debugging options in the sidebar Debugging Python Code, but at this point in the book your best bet is probably rote imitation.

Because this scheme uses shell command lines to start Python programs, all the usual shell syntax applies. For instance, you can route the output of a Python script to a file to save it for later use or inspection by using special shell syntax:

% python script1.py > saveit.txt

In this case, the three output lines shown in the prior run are stored in the file saveit.txt instead of being printed. This is generally known as stream redirection; it works for input and output text and is available on Windows and Unix-like systems. It also has little to do with Python (Python simply supports it), so we will skip further details on shell redirection syntax here.

If you are working on a Windows platform, this example works the same, but the system prompt is normally different:

C:\Python30> python script1.py
win32
1267650600228229401496703205376
Spam!Spam!Spam!Spam!Spam!Spam!Spam!Spam!

As usual, be sure to type the full path to Python if you haven’t set your PATH environment variable to include this path or run a change-directory command to go to the path:

D:\temp> C:\python30\python script1.py
win32
1267650600228229401496703205376
Spam!Spam!Spam!Spam!Spam!Spam!Spam!Spam!

On all recent versions of Windows, you can also type just the name of your script, and omit the name of Python itself. Because newer Windows systems use the Windows Registry to find a program with which to run a file, you don’t need to name “python” on the command line explicitly to run a .py file. The prior command, for example, could be simplified to this on most Windows machines:

D:\temp> script1.py

Finally, remember to give the full path to your script file if it lives in a different directory from the one in which you are working. For example, the following system command line, run from D:\other, assumes Python is in your system path but runs a file located elsewhere:

D:\other> python c:\code\otherscript.py

If your PATH doesn’t include Python’s directory, and neither Python nor your script file is in the directory you’re working in, use full paths for both:

D:\other> C:\Python30\python c:\code\otherscript.py