See the example below. 
import subprocess
p = subprocess.Popen(["ping", "localhost"], stdout=subprocess.PIPE)
output, err = p.communicate()
print  output
Output:
Pinging w10-PC [::1] with 32 bytes of data:
Reply from ::1: time<1ms 
Reply from ::1: time<1ms 
Reply from ::1: time<1ms 
Reply from ::1: time<1ms 
Ping statistics for ::1:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 0ms, Maximum = 0ms, Average = 0ms
Replace ["ping", "localhost"] in the example with 
["tesseract", "--tessdata-dir", "/usr/share", "imagename", "outputbase", "-l", "eng", "-psm", "3"].
You may further check examples here, this execute-shell-commands-in-python question and Python 2.7 doc for more information.