Last updated on 2023-05-02 | Edit this page
- How do function calls actually work?
- How can I determine where errors occurred?
- Identify local and global variables.
- Identify parameters as local variables.
- Read a traceback and determine the file, function, and line number on which the error occurred, the type of error, and the error message.
- There are only so many sensible names for variables.
- People using functions shouldn’t have to worry about what variable names the author of the function used.
- People writing functions shouldn’t have to worry about what variable names the function’s caller uses.
- The part of a program in which a variable is visible is called its scope.
= 103.9 pressure def adjust(t): = t * 1.43 / pressure temperature return temperature
pressureis a global variable.
- Defined outside any particular function.
- Visible everywhere.
temperatureare local variables in
- Defined in the function.
- Not visible in the main program.
- Remember: a function parameter is a variable that is automatically assigned a value when the function is called.
print('adjusted:', adjust(0.9)) print('temperature after call:', temperature)
Traceback (most recent call last): File "/Users/swcarpentry/foo.py", line 8, in <module> print('temperature after call:', temperature) NameError: name 'temperature' is not defined
Read the traceback below, and identify the following:
- How many levels does the traceback have?
- What is the file name where the error occurred?
- What is the function name where the error occurred?
- On which line number in this function did the error occur?
- What is the type of error?
- What is the error message?
--------------------------------------------------------------------------- KeyError Traceback (most recent call last) <ipython-input-2-e4c4cbafeeb5> in <module>() 1 import errors_02 ----> 2 errors_02.print_friday_message() /Users/ghopper/thesis/code/errors_02.py in print_friday_message() 13 14 def print_friday_message(): ---> 15 print_message("Friday") /Users/ghopper/thesis/code/errors_02.py in print_message(day) 9 "sunday": "Aw, the weekend is almost over." 10 } ---> 11 print(messages[day]) 12 13 KeyError: 'Friday'
- Three levels.
- Line 11
KeyError. These errors occur when we are trying to look up a key that does not exist (usually in a data structure such as a dictionary). We can find more information about the
KeyErrorand other built-in exceptions in the Python docs.