Another simple, albeit crude, method is to use e-mail. I e-mail my first large python program to my own e-mail address, and then read the e-mail using the e-mail App on my iPhone.

Then I started to "Reply" to the e-mail in my e-mail App, which opens the original message in a new window. I deleted the text that was added at the top of the new message, and then did "Select all" and "Copy".

After doing that, I went to the Pythonista App and used "Paste" to paste the program text into the Pythonista edit window.

Then, finally, I went back to the e-mail App and cancelled the reply message.