Why Does My Seemingly Correct Python Code Throw a 'SyntaxError: Invalid Syntax'?

Troubleshoot "SyntaxError: Invalid Syntax" in Seemingly Valid Python Code

When encountering a "SyntaxError: invalid syntax" error in a line of code that appears valid, it's prudent to check the preceding line. This error can potentially result from an imbalance of parentheses in the previous line, which can carry forward and trigger the error.

Consider the following code as an example:

fi2=0.460*scipy.sqrt(1-(Tr-0.566)**2/(0.434**2)+0.494)
guess = Pmin+(Pmax-Pmin)*((1-w**2)*fi1+(w**2)*fi2)

Here, the error is reported on line 2 for "invalid syntax." However, upon closer inspection, it becomes evident that line 1 has three open parentheses but only two closed parentheses.

open parentheses: 1  2  3        # count open parentheses
                   v  v  v       # forked lines leading to parentheses
fi2=0.460*scipy.sqrt(1-(Tr-0.566)**2/(0.434**2)+0.494)
                               ^   ^        # where error might be
closed parentheses:          1  2        # count closed parentheses

The erroneous line 1 should be corrected to:

fi2=0.460*scipy.sqrt(1-(Tr-0.566)**2/(0.434**2) + 0.494)  # add missing parenthesis

Note that in older versions of Python (pre-3.9), error messages were not as precise in identifying the location of the issue. However, in Python 3.9 and later, the error message correctly points to the source of the problem:

File "prog.py", line 1
    xyzzy = (1 +
            ^
SyntaxError: '(' was never closed

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