Use subprocess.run:
import subprocess
subprocess.run(["ls", "-l"])
Another common way is os.system but you shouldn't use it because it is unsafe if any parts of the command come from outside your program or can contain spaces or other special characters, also subprocess.run is generally more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc.). Even the documentation for os.system recommends using subprocess instead.
On Python 3.4 and earlier, use subprocess.call instead of .run:
subprocess.call(["ls", "-l"])
Use subprocess.run:
import subprocess
subprocess.run(["ls", "-l"])
Another common way is os.system but you shouldn't use it because it is unsafe if any parts of the command come from outside your program or can contain spaces or other special characters, also subprocess.run is generally more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc.). Even the documentation for os.system recommends using subprocess instead.
On Python 3.4 and earlier, use subprocess.call instead of .run:
subprocess.call(["ls", "-l"])
Here is a summary of ways to call external programs, including their advantages and disadvantages:
os.systempasses the command and arguments to your system's shell. This is nice because you can actually run multiple commands at once in this manner and set up pipes and input/output redirection. For example:os.system("some_command < input_file | another_command > output_file")However, while this is convenient, you have to manually handle the escaping of shell characters such as spaces, et cetera. On the other hand, this also lets you run commands which are simply shell commands and not actually external programs.
os.popenwill do the same thing asos.systemexcept that it gives you a file-like object that you can use to access standard input/output for that process. There are 3 other variants of popen that all handle the i/o slightly differently. If you pass everything as a string, then your command is passed to the shell; if you pass them as a list then you don't need to worry about escaping anything. Example:print(os.popen("ls -l").read())subprocess.Popen. This is intended as a replacement foros.popen, but has the downside of being slightly more complicated by virtue of being so comprehensive. For example, you'd say:print(subprocess.Popen("echo Hello World", shell=True, stdout=subprocess.PIPE).stdout.read())instead of
print(os.popen("echo Hello World").read())but it is nice to have all of the options there in one unified class instead of 4 different popen functions. See the documentation.
subprocess.call. This is basically just like thePopenclass and takes all of the same arguments, but it simply waits until the command completes and gives you the return code. For example:return_code = subprocess.call("echo Hello World", shell=True)subprocess.run. Python 3.5+ only. Similar to the above but even more flexible and returns aCompletedProcessobject when the command finishes executing.os.fork,os.exec,os.spawnare similar to their C language counterparts, but I don't recommend using them directly.
The subprocess module should probably be what you use.
Finally, please be aware that for all methods where you pass the final command to be executed by the shell as a string and you are responsible for escaping it. There are serious security implications if any part of the string that you pass can not be fully trusted. For example, if a user is entering some/any part of the string. If you are unsure, only use these methods with constants. To give you a hint of the implications consider this code:
print(subprocess.Popen("echo %s " % user_input, stdout=PIPE).stdout.read())
and imagine that the user enters something "my mama didnt love me && rm -rf /" which could erase the whole filesystem.
Videos
os.system("sudo python scale1.py")
first you will need to import the os module
import os
I don't have a pi with me atm to test, but this comes from the second answer to this question: https://stackoverflow.com/questions/89228/calling-an-external-command-in-python
In general, use the subprocess module
subprocess.call(["sudo","python","scale1.py"])
for command line calls.
An example processing the result of a subprocess call;
result = subprocess.check_output(['sudo','service','mpd','restart'])
Subprocess replaces several older modules and functions, like os.system and os.spawn. It does a good job in sanitizing arguments, so it protects you from shell injection.
https://docs.python.org/2/library/subprocess.html
Of course to run a second python script there is no need for CLI call, you can import those.