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Page References

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Micro Python Tutorial Exercise 02
MicroPythonTutorialExercise02

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At line 1 changed one line
!!! Blocks
!!! Functions
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%%info
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%%
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In Python, a __block__ is a group of statements that belong together, forming the body of a function, loop, class or other structure. A block is defined by an initial line followed by the contents of the block indented four characters.
We can define __functions__ in Python. Functions are defined globally, within the file/module as they begin in column 0.
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As an example, a {{for}} block sets up a loop:
%%filename main.py %% %%python
for i in range(0,5):
print(i)
%%
%%warning
Notice that the contents of the {{for}} block are indented four characters. This causes the contents of the block to be executed five times, printing the value of the index variable ("i") each time.
%%
!! The try-except-finally Block
There is a {{try-except-finally}} structure called a __compound statement__, consisting of three separate __blocks__. This is ideal for a main.py file, and is also a very common and useful structure. It is composed of three parts:
* {{try}}: this block contains is the code we want to ''try'' to execute
* {{except}}: this block catches any errors or exceptions that occur and executes the block, handling the exception
* {{finally}}: no matter what happens, this block will be executed after the {{try}} (and possibly {{except}}) blocks are executed
In the below example, there is a {{try}} block, followed by an {{except}} block, followed by a {{finally}} block. A {{try}} block must be followed by an {{except}} block and/or a {{finally}} block (you must have one of them).
%%filename main.py %%
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try:
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print('hello world.') # remember to indent the insides of your blocks by 4 characters!
def display_message(message):
print(message)
raise Exception('we did something wrong.')
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except Exception:
# this block is executed if there is an exception (error)
print('an error occurred.')
finally:
# this is always executed, no matter what
print('complete.')
%%
If you want to use the exception to print out an error message you need to assign it to a variable (in this case, we've used {{ex}}).
%%filename main.py %%
%%python
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print('hello world.')
except Exception as ex: # we assign the Exception to the variable 'ex'
print('an error occurred: {}'.format(ex))
finally:
print('complete.')
%%
!! Optional Blocks
As mentioned above, in the {{try-except-finally}} compound statement, the {{except}} or {{finally}} block is optional.
If you don't need to do anything after exiting the {{try}} block you can leave off the {{finally}} block:
%%filename main.py %%
%%python
try:
print('hello world.')
display_message('hello world.')
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print('an error occurred.')
%%
or, just using {{finally}}:
%%filename main.py %%
%%python
try:
print('hello world.')
print('an error occurred: {}'.format(e))
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This would be useful when you want the Exception to be passed on and handled somewhere else.
----
__Previous:__ [MicroPython Tutorial Exercise 1|MicroPythonTutorialExercise01]: main.py \\
__Next:__ [MicroPython Tutorial Exercise 3|MicroPythonTutorialExercise03]: functions
This page (revision-17) was last changed on 2025-08-01 12:57 by Murray AltheimTop