Encrypting to One Key

Once the the Context is set the main issues with encrypting data is essentially reduced to key selection and the keyword arguments specified in the gpg.Context().encrypt() method.

Those keyword arguments are:

recipients, a list of keys encrypted to (covered in greater detail in the following section);
sign, whether or not to sign the plaintext data, see subsequent sections on signing and verifying signatures below (defaults to True);
sink, to write results or partial results to a secure sink instead of returning it (defaults to None);
passphrase, only used when utilising symmetric encryption (defaults to None);
always_trust, used to override the trust model settings for recipient keys (defaults to False);
add_encrypt_to, utilises any preconfigured encrypt-to or default-key settings in the user's gpg.conf file (defaults to False);
prepare, prepare for encryption (defaults to False);
expect_sign, prepare for signing (defaults to False);
compress, compresses the plaintext prior to encryption (defaults to True).

import gpg

a_key = "0x12345678DEADBEEF"
text = b"""Some text to test with.

Since the text in this case must be bytes, it is most likely that
the input form will be a separate file which is opened with "rb"
as this is the simplest method of obtaining the correct data
format.
"""

c = gpg.Context(armor=True)
rkey = list(c.keylist(pattern=a_key, secret=False))
ciphertext, result, sign_result = c.encrypt(text, recipients=rkey, sign=False)

with open("secret_plans.txt.asc", "wb") as f:
    f.write(ciphertext)

Though this is even more likely to be used like this; with the plaintext input read from a file, the recipient keys used for encryption regardless of key trust status and the encrypted output also encrypted to any preconfigured keys set in the gpg.conf file:

import gpg

a_key = "0x12345678DEADBEEF"

with open("secret_plans.txt", "rb") as f:
    text = f.read()

c = gpg.Context(armor=True)
rkey = list(c.keylist(pattern=a_key, secret=False))
ciphertext, result, sign_result = c.encrypt(text, recipients=rkey,
                                            sign=True, always_trust=True,
                                            add_encrypt_to=True)

with open("secret_plans.txt.asc", "wb") as f:
    f.write(ciphertext)

If the recipients paramater is empty then the plaintext is encrypted symmetrically. If no passphrase is supplied as a parameter or via a callback registered with the Context() then an out-of-band prompt for the passphrase via pinentry will be invoked.