Understanding Gekko’s Syntax Error: Missing Opening Parenthesis

What will you learn?

In this tutorial, you will delve into a prevalent issue encountered while utilizing the Gekko library in Python: the syntax error message indicating “Error in syntax of function string: Missing opening parenthesis.” You will gain insights on identifying and resolving this error to ensure smooth execution of your code.

Introduction to Problem and Solution

Encountering the “Missing opening parenthesis” error within Gekko often signifies discrepancies in defining functions or equations within your model. This could stem from overlooking an opening parenthesis or inaccurately formatting a function call during model setup.

To address this, we follow a systematic approach: 1. Reviewing Function Syntax: Validate that each function call aligns with Gekko’s expected format. 2. Debugging Step by Step: Methodically inspect model equations and function calls for any missing parentheses or syntactical errors.

By adopting this methodical strategy, we pinpoint and rectify the root cause of the error, ensuring the seamless operation of our model.


To tackle a missing opening parenthesis, meticulously examine your code for potential instances where this omission might occur. Here is an illustrative snippet:

from gekko import GEKKO

m = GEKKO()    
x = m.Var(value=0)
y = m.Var(value=0)

# Incorrect usage that may lead to an error
m.Equation(y == x**2 + 3*x + 2)

# Corrected version
m.Equation(y == x**2 + 3*x + 2)

# Copyright PHD

Ensure adherence to proper Python syntax in all operations, particularly those involving equations and functions within GEKKO().


When processing your model, Gekko translates Python commands into its internal language for optimization. An absence of an opening parenthesis disrupts this translation process, leading to parsing errors and triggering the mentioned syntax issue.

Key Points: – Syntax Precision: Minute errors can impact your entire model. – Parentheses Significance: Crucial for delineating operation order and function calls; their absence hinders parsing. – Incremental Debugging: Test segments of your code iteratively to isolate errors effectively.

  1. How can I efficiently check my entire code for syntax errors?

  2. Utilize linter tools like pylint or flake8 tailored for Python codes. These tools not only detect missed parentheses but also highlight other potential issues affecting your code’s style or logic.

  3. Are comments permissible within GEKKO models?

  4. Yes, you can incorporate Python comments (#) outside actual GEKKO commands; however, ensure they do not interfere with equation definitions or variable assignments within GEKKO methods.

  5. Do all Gekko functions necessitate parentheses?

  6. Yes, akin to standard Python conventions, all function calls in Gekko require parentheses around arguments even if single argument is involved.

  7. How can complex models in Gekko be debugged effectively?

  8. Break down intricate equations into smaller components for individual testing before reassembling them. Employ print statements strategically around suspected problematic areas; intermediate values often offer clues towards resolving larger issues.

  9. Is indentation crucial in rectifying such syntax errors?

  10. While indentation does not directly relate to missing parentheses errors unless indirectly leading up to it via misinterpretation of code blocks (especially within conditionals/loops), proper indentation enhances readability facilitating easier debugging overall.

  11. Besides ‘Missing opening parenthesis,’ what triggers ‘Unknown keyword’ errors?

  12. These errors typically arise from typos when invoking built-in methods/functions from Gekko or other libraries or attempting unauthorized access on objects not exposed by these libraries’ APIs.

  13. Can disregarding warnings escalate towards critical failures like these?

  14. Warnings themselves do not halt execution immediately as errors do; however, they indicate potential misuse/misunderstanding of certain functionalities which if unaddressed could contribute towards logical/runtime bugs later on.


Understanding common syntactical pitfalls such as overlooking essential characters like “(” proves instrumental in expediting debugging processes inherent in modeling tasks employing frameworks like Gekko. Embrace incremental development/testing phases while leveraging community resources/forums dedicated to scientific computing/python programming paradigms when faced with challenges!

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