You never moved the pexpect cursor forward. sys.stdout.buffer echoed the prompt, so that is what before displayed. Comment out child.logfile_read = sys.stdout.buffer, and you will just get b''.
To move the buffer forward, you have two options:
NOTE - Tested on Ubuntu 20.04 using Python 3.8
1. If you do not have to enter any more data, use child.read() to let the program run; the cursor will automatically move forward. Once read encounters an EOF (program termination), logfile_read will display all the output to STDOUT:
Parent (parent.py):
import pexpect
import sys
# helium-wallet.py is just a quick script I wrote to mimic your script
print("Parent: Running the child.")
child = pexpect.spawn("python3 helium-wallet.py")
child.logfile_read = sys.stdout.buffer
child.expect("Space separated seed words: ")
child.sendline("carpet again stick economy finish recipe blouse forward program stumble need ginger")
child.read()
print("Parent: Script complete. Have a nice day.")
Child (helium-wallet.py):
text = input("Child: Space separated seed words: ")
print("Child: Did something with:", text)
print("Child: Script complete. Have a nice day.")
Output:
Parent: Running the child.
Child: Space separated seed words: carpet again stick economy finish recipe blouse forward program stumble need ginger
Child: Did something with: carpet again stick economy finish recipe blouse forward program stumble need ginger
Child: Script complete. Have a nice day.
Parent: Script complete. Have a nice day.
2. If you have more data to enter (i.e., you need the child to stay alive), use child.expect() (I removed the logfile echo; using it with before clutters the output):
Parent (parent.py):
import pexpect
# helium-wallet.py is just a quick script I wrote to mimic your script
print("Parent: Running the child.")
child = pexpect.spawn("python3 helium-wallet.py")
child.expect("Space separated seed words: ")
child.sendline("carpet again stick economy finish recipe blouse forward program stumble need ginger")
child.expect("Requesting more data: ")
# Now you can use before to see the results of the first input,
# since you moved the cursor forward with pexpect.expect.
print()
print("First input results:")
print("Before:", child.before)
print("Match:", child.match)
print("After:", child.after)
print()
child.sendline("Here's more data!")
output = child.read()
print("Remaining output (including your input):\n", output.decode())
print("Parent: Script complete. Have a nice day.")
Child (helium-wallet.py):
text = input("Child: Space separated seed words: ")
print("Child: Did something with:", text)
text2 = input("Child: Requesting more data: ")
print("Child: Did something else with:", text2)
print("Child: Script complete. Have a nice day.")
Output:
Parent: Running the child.
First input results:
Before: b'carpet again stick economy finish recipe blouse forward program stumble need ginger\r\nChild: Did something with: carpet again stick economy finish recipe blouse forward program stumble need ginger\r\nChild: '
Match: <re.Match object; span=(204, 226), match=b'Requesting more data: '>
After: b'Requesting more data: '
Remaining output (including your input):
Here's more data!
Child: Did something else with: Here's more data!
Child: Script complete. Have a nice day.
Parent: Script complete. Have a nice day.
BTW, to avoid output clutter, I would use either the one-time child.logfile_read = sys.stdout.buffer, or print(child.before) after each expect, but not both. In your case, I suggest using child.before to capture output only.
Good luck coding!
