import re
line = "[ choice A | choice B ] and choose between [ choice D | choice F ]"
line = re.sub(r"\[\s*([^][|]*?)\s*\|[^][]*]", r"\1", line)
print(line)
aW1wb3J0IHJlCmxpbmUgPSAiWyBjaG9pY2UgQSB8IGNob2ljZSBCIF0gYW5kIGNob29zZSBiZXR3ZWVuIFsgY2hvaWNlIEQgfCBjaG9pY2UgRiBdIgpsaW5lID0gcmUuc3ViKHIiXFtccyooW15dW3xdKj8pXHMqXHxbXl1bXSpdIiwgciJcMSIsIGxpbmUpCnByaW50KGxpbmUp