Avoiding Crashes, Try...except ,You are a Software Developer! , Traceback

Avoiding Crashes

Sometimes, we just can't code around a crash. It's coming anyway, and all you can do is brace for impact.
Until now!
Let's look at an example based on yesterday's lesson.

👉 In this example, if the 'Stuff.mine' file doesn't exist, then the code will throw a 'no such file' error.

myStuff = []
f.open("Stuff.mine","r")
myStuff = eval(f.read())
f.close()
for row in myStuff:
print(row)

Try...except

The new construct to get around this is called try.... except
All the code that should work goes inside the try.

The error messages/instructions to handle any errors running the try code go inside the except

👉 Like this:

myStuff = []

try:

f.open("Stuff.mine","r")

myStuff = eval(f.read())

f.close()

# Try to find a file called 'Stuff.mine' and open it

except:

print("ERROR: Unable to load")

# If the file can't be found, show the error instead of crashing the whole program

for row in myStuff:

print(row)

You are a Software Developer!

try.... except is great for improving the user experience to reduce frustration.
However, there are problems with just putting the whole code in a 'try except'.
As developers (yes you are a software developer now), it'd be nice to know what sort of error has occurred so that we have a better idea of how to fix it

We can tell except what type of error(s) to look for. Exception (capital 'E') means 'every type'. I've captured the error type in the 'err' variable and printed it out to tell me what the error is. Here's a list of some built in except error codes

👉 Look at how I've extended the except now.

myStuff = []

try:

f.open("Stuff.mine","r")

myStuff = eval(f.read())

f.close()

# Try to find a file called 'Stuff.mine' and open it

except Exception as err:

print("ERROR: Unable to load")

print(err)

for row in myStuff:

print(row)

Traceback

We could even get rid of the 'err' variable entirely and print a traceback, which will show you the red error tracing you see when python crashes.

I've created a 'debugMode' variable at the top of my code and pu the traceback in an if inside the except.

👉 This lets me show/hide the tracebacks easily by setting debugMode to True/False:

debugMode = True

myStuff = []

try:

f.open("Stuff.mine","r")

myStuff = eval(f.read())

f.close()

# Try to find a file called 'Stuff.mine' and open it

except Exception:

print("ERROR: Unable to load")

if debugMode:

print(traceback)

for row in myStuff:

print(row)

Comments

CONTINUE COMMAND AND EXIT LINE

The Continue Command The continue command stops executing code in the loop and starts at the top of the loop again. Essentially, we want to kick the user back to the original question. EXAMPLE : while True: print("You are in a corridor, do you go left or right?") direction = input("> ") if direction == "left": print("You have fallen to your death") break elif direction == "right": continue else: print("Ahh! You're a genius, you've won") NOTE : The else statement refers to any input besides left or right (up or esc). Since the user is a winner, we do not want to use break or it would say they have failed. EXIT COMMAND LINE The previous code continues to loop even after the user has won. Let's fix that with the exit() command EXAMPLE: print("Let's play chutes and ladders. Pick ladder or chute.") while...

FOR LOOP , RANGE

FOR LOOP A while loop is perfect to use when we don't know how many times we want the loop to repeat. If we have an idea of how many times we want the loop to repeat, we can use a for loop to loop code in exactly the same way the while loop did. EXAMPLE : for counter in range(10): print(counter) RANGE The range function creates a list of numbers in the range you create. If you only give it one number, it will start at 0 and move to a state where the final number is one less than the number in the brackets. In this case, the final number would be 9 . EXAMPLE : total = 0 for number in range(100) : total += number print(total)

Automate! Automate!

Making this customizable 👉So how about making our search user customizable? In the code below, I have: Asked the user to input an artist (line 14) Tidied up their input (line 15) formatted the search URL as an fString that includes the artist (line 19) Here's tAutomate! Automate! We are so close. I can taste it, folks! Massive kudos on getting this far! Today's lesson, however, will work best if you have one of Replit's paid for features (hacker plan or cycles). Free plan Repls 'fall asleep' after a while. Automation kinda relies on the Repl being always on. If you have hacker plan or you've bought some cycles, then you can enable always on in the drop down menu that appears when you click your Repl name (top left).he code: This is important because when our repl is always running, it can keep track of time and schedule events. 👉 I've set up a simple schedule that prints out a clock emoji every couple of seconds. It works like this: Import schedule librar...

PYTHON SYNTAX