Ask the right questions to secure the right Cython talent among an increasingly shrinking pool of talent.

Cython is a programming language designed to bridge the gap between Python and C/C++. It was developed by Robert Bradshaw, Stefan Behnel, Dag Sverre Seljebotn, Greg Ewing and others in 2007 as an optimization to Python's execution speed. Cython allows for both static and dynamic typing, enabling developers to write C extensions for Python in a more straightforward manner. The language has been widely adopted due its ability to handle computationally intensive tasks with ease. Its development is open-source under the Apache License which encourages community contributions.

First 20 minutes

General Cython knowledge and experience

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

What are the ways to declare C variables in Cython?

C variables can be declared in Cython using the 'cdef' keyword followed by the type and the variable name.

How would you compile a Cython file?

You can compile a Cython file by using the command 'cython filename.pyx' which will generate a .c file. You then compile this .c file with a C compiler.

Describe the difference between Python and Cython.

Python is an interpreted language while Cython is a programming language that aims to be a superset of Python to also include calling C functions and declaring C types on variables and class attributes.

What are the main benefits of using Cython?

Cython can increase the execution speed of Python code and allow the calling of C functions. It also provides type safety.

How would you install Cython on your system?

You can install Cython using pip, the Python package installer. The command is 'pip install Cython'.

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What youre looking for early-on

Does the candidate have experience with multi-threading in Cython?

Cython supports multi-threading, which can be used to further optimize code. A good candidate should have experience with this.

Has the candidate shown an ability to work with Python's C API?

Working with Python's C API is often necessary when using Cython, so a good candidate should be comfortable with this.

Is the candidate familiar with the process of optimizing Python code with Cython?

One of the main uses of Cython is to optimize Python code, so a good candidate should be familiar with this process.

Can the candidate effectively debug Cython code?

Debugging Cython code can be more complex than debugging Python code due to the interaction between Python and C. A good candidate should be able to handle this.

Has the candidate demonstrated experience with Cython-specific concepts?

This includes concepts such as static typing, cdef functions, and interfacing with C code. This is important as it shows the candidate's depth of knowledge in Cython.

Does the candidate have a strong understanding of both Python and C?

Cython is a superset of Python that additionally supports calling C functions and declaring C types. Therefore, a strong understanding of both Python and C is crucial.

Next 20 minutes

Specific Cython development questions

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

What are the limitations of using Cython?

One limitation of Cython is that it can make the code harder to read and write. It also requires a compilation step which makes the development process slower.

How would you improve the performance of Python code using Cython?

You can improve the performance of Python code using Cython by declaring types for variables, converting Python classes to C classes, and calling C functions directly.

What is the role of the 'pyx' file extension in Cython?

The 'pyx' file extension is used for Cython source files. These files contain code that is a mix of Python and C.

Describe the difference between 'cdef' and 'cpdef' in Cython.

'cdef' is used to declare C variables, functions, and classes. 'cpdef' is used to declare C functions that can be called from Python and C.

How would you call a C function from a Cython file?

You can call a C function from a Cython file by using the 'cdef extern' keyword to declare the function and then simply call it as you would in Python.

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A skilled Cython engineer should possess strong knowledge of Python and C, as well as the ability to integrate Python with existing C code. They should also have experience optimizing Python code with Cython. Red flags could include inability to explain how Cython improves Python performance or lack of practical experience.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Cython.

What does this simple Cython code do?def add_numbers(int a, int b):
    return a + b
This code defines a function in Cython that adds two integers together and returns the result.
What does the 'cdef' keyword do in this Cython code?cdef int a = 5
print(a)
The 'cdef' keyword is used to declare C variables. In this code, it is used to declare an integer 'a' with a value of 5.
What will be the output of this Cython code that manipulates an array?cdef int[:] arr = [1, 2, 3, 4, 5]
arr[2] = 10
print(arr)
This code will output the array [1, 2, 10, 4, 5]. It creates an array and then changes the third element to 10.
What does this Cython code do that involves threading?from cython.parallel import prange
cdef int i
for i in prange(5, nogil=True):
    print(i)
This code uses the 'prange' function from the 'cython.parallel' module to create a parallel for loop that runs 5 iterations concurrently. It prints the index of each iteration.
What does this Cython code do that involves class design?cdef class MyClass:
    cdef int a, b
    def __init__(self, int a, int b):
        self.a = a
        self.b = b
    def add(self):
        return self.a + self.b
This code defines a Cython class 'MyClass' with two integer attributes 'a' and 'b'. It has an '__init__' method to initialize these attributes and an 'add' method to add these two numbers and return the result.
What will be the output of this advanced Cython code?cdef int a = 5
b = a
b += 5
print(a, b)
This code will output '5 10'. It declares an integer 'a' with a value of 5, assigns this value to 'b', increments 'b' by 5, and then prints both 'a' and 'b'. The value of 'a' remains unchanged because 'b' is a separate copy of 'a'.

Wrap-up questions

Final candidate for Cython role questions

The final few interview questions for a Cython candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.

What is the process to convert a Python project to Cython?

To convert a Python project to Cython, you would need to rename your .py files to .pyx, add type declarations to your variables and functions, and compile your .pyx files into .c files.

How would you use Python libraries in Cython?

Python libraries can be used in Cython by simply importing them as you would in Python.

What is the purpose of the 'cimport' statement in Cython?

The 'cimport' statement is used to import C functions, types, and variables from .pxd files.

How would you handle exceptions in Cython?

Exceptions in Cython can be handled using the same 'try' and 'except' blocks as in Python. Cython also supports the 'finally' block.

Describe the difference between 'cdef' and 'def' functions in Cython.

'cdef' functions are C functions and can't be called from Python, while 'def' functions are Python functions and can be called from both Python and C.

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Cython application related

Product Perfect's Cython development capabilities

Beyond hiring for your Cython engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Cython projects, and can engage in multiple capacities.

Cython Consultive assessments

Cython Application Conversion Assessment Cython Application Integration Assessment Cython Data & Database Integration Assessment

Custom Cython development projects

Custom Cython App Conversion Cython Custom App Development Process App UI Design for Cython Facelifts

Cython Developer Hiring Guide

Hiring Guide for Cython Engineers

First 20 minutes

General Cython knowledge and experience

What are the ways to declare C variables in Cython?

How would you compile a Cython file?

Describe the difference between Python and Cython.

What are the main benefits of using Cython?

How would you install Cython on your system?

What youre looking for early-on

Does the candidate have experience with multi-threading in Cython?

Has the candidate shown an ability to work with Python's C API?

Is the candidate familiar with the process of optimizing Python code with Cython?

Can the candidate effectively debug Cython code?

Has the candidate demonstrated experience with Cython-specific concepts?

Does the candidate have a strong understanding of both Python and C?

Next 20 minutes

Specific Cython development questions

What are the limitations of using Cython?

How would you improve the performance of Python code using Cython?

What is the role of the 'pyx' file extension in Cython?

Describe the difference between 'cdef' and 'cpdef' in Cython.

How would you call a C function from a Cython file?

The ideal back-end app developer

What you’re looking to see on the Cython engineer at this point.

What does this simple Cython code do?

This code defines a function in Cython that adds two integers together and returns the result.

What does the 'cdef' keyword do in this Cython code?

The 'cdef' keyword is used to declare C variables. In this code, it is used to declare an integer 'a' with a value of 5.

What will be the output of this Cython code that manipulates an array?

This code will output the array [1, 2, 10, 4, 5]. It creates an array and then changes the third element to 10.

What does this Cython code do that involves threading?

This code uses the 'prange' function from the 'cython.parallel' module to create a parallel for loop that runs 5 iterations concurrently. It prints the index of each iteration.

What does this Cython code do that involves class design?

This code defines a Cython class 'MyClass' with two integer attributes 'a' and 'b'. It has an '__init__' method to initialize these attributes and an 'add' method to add these two numbers and return the result.

What will be the output of this advanced Cython code?

This code will output '5 10'. It declares an integer 'a' with a value of 5, assigns this value to 'b', increments 'b' by 5, and then prints both 'a' and 'b'. The value of 'a' remains unchanged because 'b' is a separate copy of 'a'.

Wrap-up questions

Final candidate for Cython role questions

What is the process to convert a Python project to Cython?

How would you use Python libraries in Cython?

What is the purpose of the 'cimport' statement in Cython?

How would you handle exceptions in Cython?

Describe the difference between 'cdef' and 'def' functions in Cython.

Cython Consultive assessments

Custom Cython development projects

This code defines a Cython class 'MyClass' with two integer attributes 'a' and 'b'. It has an 'init' method to initialize these attributes and an 'add' method to add these two numbers and return the result.