How to convert a string into a set of keystrokes in python on OS

How to convert a string into a set of keystrokes in python on OSX

Given a string, I'd like to be able to send a set of keystrokes to type that string and I'd like to be able to do it in python on OSX (in python because it's part of a larger project already written in python, on OSX because I am trying to port it to OSX).

I'm able to do this now using pyobj like so (this is somewhat simplified):

from Quartz import *

CHAR_TO_SEQUENCE = {
    'a':[(0, True), (0, False)]
}

def send_string(string):
    for c in string:
        sequence = CHAR_TO_SEQUENCE[c]
        for keycode, key_down in sequence:
            CGEventPost(kCGSessionEventTap, CGEventCreateKeyboardEvent(None, keycode, key_down))

and I've fleshed out CHAR_TO_SEQUENCE to include most of what I can type on my keyboard, which took a while and was tedious.

The problems with this are: - It only works while the keyboard has the ANSII standard layout. If someone uses a french keyboard, for example, it will type the wrong things. - It requires this ridiculous table.

The API mentioned there doesn't seem to be available via pyobj (or maybe I just couldn't figure out the import path).

I've seen some suggestions to set CGEventKeyboardSetUnicodeString to the desired string and not worry about the keycode. But I wasn't able to figure out how to call CGEventKeyboardSetUnicodeString from python (I can't get the arguments right) and it's not clear that this will work because the documentation says that applications can choose to ignore this in favor of the keycode.

Is there a way to do this in python on OSX?

Answer

Yes, there is a way to send keystrokes programmatically to simulate typing a string on macOS using Python. You can use the Quartz framework in Python, but as you correctly pointed out, there are some challenges when it comes to handling different keyboard layouts and dealing with keycodes directly.

Instead of manually managing keycodes for each character (which is prone to errors and tedious), you can leverage the CGEventKeyboardSetUnicodeString method, which allows you to send Unicode strings directly. This way, you don't need to worry about keycodes, and the string will be typed correctly regardless of the keyboard layout.

Here’s a solution that makes use of the CGEventKeyboardSetUnicodeString method. To do this, you'll need to call the appropriate Quartz APIs from Python, but you'll have to handle the function signature and data types carefully.

Steps to simulate typing a string in Python on macOS:

1. Import necessary libraries: You’ll need Quartz (part of the pyobjc-framework-Quartz package) to interact with the macOS API.

2. Set up the CGEventKeyboardSetUnicodeString function: This function allows sending Unicode characters directly, bypassing the need for keycodes.

3. Use a loop to send the string: Loop over the string and send each character.

Here is a complete solution using pyobjc:

Solution Using CGEventKeyboardSetUnicodeString

from Quartz.CoreGraphics import *
import time

def send_string(string):
    # Create an empty event of type keyboard event
    event = CGEventCreateKeyboardEvent(None, 0, True)  # 'True' means key press
    
    # Set the Unicode string to be sent
    CGEventKeyboardSetUnicodeString(event, len(string), string)
    
    # Post the event to the event stream
    CGEventPost(kCGEventKeyDown, event)
    
    # To simulate key release event, we can create a key release event and post it
    event = CGEventCreateKeyboardEvent(None, 0, False)  # 'False' means key release
    CGEventKeyboardSetUnicodeString(event, len(string), string)
    CGEventPost(kCGEventKeyUp, event)

def main():
    test_string = "Hello, World!"
    send_string(test_string)
    time.sleep(0.5)  # Sleep to observe results before the script finishes

if __name__ == "__main__":
    main()

Explanation:

1. CGEventCreateKeyboardEvent: This function creates a keyboard event. The second argument is the keycode, but it's irrelevant when you're using CGEventKeyboardSetUnicodeString to set a Unicode string.

2. CGEventKeyboardSetUnicodeString: This method sets the Unicode string to the event. It takes the length of the string and the string itself as parameters. This is the key function that allows you to type a string directly.

3. Posting the event: We post both key down (kCGEventKeyDown) and key up (kCGEventKeyUp) events to simulate pressing and releasing keys.

4. Keyboard Layout Independence: This approach doesn’t rely on keycodes, so it works with any keyboard layout, as it sends the exact Unicode characters to the system.

Key Points:

• Unicode String: By using CGEventKeyboardSetUnicodeString, you bypass the need to worry about keycodes entirely. This allows you to simulate typing a string in any layout or language, which is a huge improvement over manually setting keycodes.

• Post Key Down and Key Up Events: Both key down and key up events are posted to simulate actual typing behavior (press and release of keys).

• Delay (time.sleep): Adding a small delay after sending the string can be useful for debugging, especially when you're trying to observe the simulated typing behavior.

Limitations and Considerations:

• Applications ignoring Unicode: Some applications may not respect the UnicodeString if they opt to handle keycodes differently. However, this is generally rare for most applications.

• Permissions: macOS may require you to grant your Python script accessibility permissions to simulate keystrokes. Make sure to grant access under System Preferences > Security & Privacy > Privacy > Accessibility.

Alternative (Manually Handling Keycodes)

If you still need to simulate key presses using keycodes (for more complex interactions, like modifier keys), you can create a more complex CHAR_TO_KEYCODE mapping and use CGEventCreateKeyboardEvent and CGEventPost to send each keystroke manually.

However, using CGEventKeyboardSetUnicodeString is generally simpler and more reliable for text input.

Let me know if you have any questions or need further clarification!