The Python interpreter is usually installed as `/usr/local/bin/python
'
on those machines where it is available; putting `/usr/local/bin
' in
your Unix shell's search path makes it possible to start it by
typing the command
pythonto the shell. 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.)
Typing an EOF character (Control-D on Unix, Control-Z or F6 on DOS
or 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 commands: import sys ;
sys.exit()
.
The interpreter's line-editing features usually aren't very
sophisticated. On Unix, whoever installed the interpreter may have
enabled support for the GNU readline library, which adds more
elaborate interactive editing and history features. 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 A 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 third 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 best to quote
command
in its entirety with double quotes.
Note that there is a difference between `python file' and
`python <file'. In the latter case, input requests from the
program, such as calls to input()
and raw_input()
, are
satisfied from file. Since this file has already been read
until the end by the parser before the program starts executing, the
program will encounter EOF immediately. In the former case (which is
usually what you want) they are satisfied from whatever file or device
is connected to standard input of the Python interpreter.
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
before the script. (This does not work if the script
is read from standard input, for the same reason as explained in the
previous paragraph.)
guido@CNRI.Reston.Va.US