Console bridge: text in, text out: recap

print(...) shows a line of text and moves to a new line. Text goes inside quotes; the quotes are not shown. A name without quotes is a stored value, so print(name) shows what is stored, and print("name") shows the word name.

+ between two pieces of text joins them with nothing in between. A space only appears if it is typed inside the quotes.

input("question") shows the question in the console, waits for the person to type and press Enter, and gives back what they typed as text. Store it with name = input(...) so later lines can use it.

Whatever is typed comes back as text, even digits. The next lessons deal with numbers.

+ joins text to text, and adds a number to a number, but will not mix them. To join a number onto text, turn it into text first: str(score) gives back a text copy, such as "5". The number itself stays a number.

Calculations can go inside: str(cups * price).

input() always gives back text. int(text) turns text made of digits into a whole number, so + adds instead of joins, and * multiplies instead of repeating text. Convert once, as the answer is stored: age = int(input("Age? ")).

A number joined onto text still needs str, as in the last lesson.

int("twelve") stops the program with an error, so a careful program checks first. text.isdigit() asks the text whether it is all digits and gives back True or False, which an if uses. The dot means "ask this text": the same shape appears for many questions you can ask a piece of text.

The pattern is: store the text, check it, convert inside the if, and reply in the else.

while condition: checks the condition. If it is true, the indented lines run, and then it checks again. If it is false, the lines are skipped and the program carries on after the loop.

Something inside the loop must be able to change the condition, usually by asking again with input. If nothing changes, the loop never ends.

total += n means "add n to what total already holds" and is short for total = total + n. A running total is set to 0 once before the loop, then changed on every pass. If it were set to 0 inside the loop, every pass would start again from nothing.

The loop's condition can read the total, or the loop can wait for a special answer such as 0 to finish.

A longer program is easier to read once you split it into jobs: set up (the secret and the first guess), the loop (keep asking until the guess is right), the check and hint inside the loop, and the count. Each job uses a move from an earlier lesson.

The secret comes from random.randint(1, 20), which gives a random whole number from 1 to 20. For now it is a recipe to copy.

while True: is a loop whose condition is never false, so it only ends when a break runs. A menu fits: show the choices, read one, do it, and go round again. if / elif / else picks what to do for each choice, and else catches anything else.

break leaves the loop it is in, not only the if. The program continues with the first line after the loop.

A test case is an input and the reply you expect. print(reply("9") == "Please choose 1 or 2.") calls the function with that input and shows True if the reply is exactly what was expected.

Good tests include normal cases and wrong ones. A test that shows False means either the code or the test is wrong: read both.

A bigger app is the small moves working together: a loop keeps the menu going, if / elif / else picks what to do, isdigit checks typed numbers, += builds the total and break ends the loop. A function gives back the replies so they can be tested.

A good plan is the theme, the choices, what is stored, and what ends it.