I know this is a controversial take. Stay with me.
LeetCode is not bad. Practicing algorithms is not bad. But if LeetCode is the only thing you are doing to prepare for Python technical interviews, you have a gap.
Here is the gap.
What LeetCode Trains
LeetCode trains you to write solutions to known problem categories. Sliding window. Two pointers. Dynamic programming. Binary search. You learn patterns and apply them.
This is genuinely useful. Interviewers do ask algorithm questions.
But there is a second type of question that LeetCode does not prepare you for at all.
The Question LeetCode Does Not Cover
data = {"a": 1, "b": 2, "c": 3}
result = {v: k for k, v in data.items() if v > 1}
print(result)
"What does this print?"
This is a dry-run question. You are not writing an algorithm. You are reading existing code and predicting its exact output. No running it. No IDE. Just you and the code.
Phone screens at Amazon, Google, Stripe, and most mid-size product companies include at least one question like this. Some interviews are entirely this format.
Why Companies Use Dry-Run Questions
They are more information-dense than algorithm questions.
A candidate who can trace 15 lines of Python under pressure demonstrates:
- Genuine Understanding: Clear mastery of Python execution, not just syntax.
- State Tracking: The ability to hold multiple state changes in mind simultaneously.
- Core Literacy: Comfort with concepts like scope, mutability, and iteration order.
- Composure: Emotional control when the answer is not immediately obvious.
Memorizing patterns works on LeetCode because the pattern is the answer. Dry-run questions have no patterns to memorize. Every snippet is different. The only thing that helps is a genuine understanding of how Python executes code.
The Answer to the Question Above
The actual output is:
{2: 'b', 3: 'c'}
The dictionary comprehension inverts the key-value pairs, filtering to only values greater than 1. So "b": 2 becomes 2: "b" and "c": 3 becomes 3: "c". The entry "a": 1 is excluded because it fails the conditional check.
If you got that right, you understand dictionary comprehensions deeply enough to predict their output, not just write them from scratch. If you got it wrong, that is the exact gap you need to close.
How to Add Dry-Run Practice to Your Routine
It takes just 15 minutes per day.
Find a complex Python snippet. Cover the output. Write your prediction down on paper. Run it and compare. Dive deep into any discrepancy you find.
If you want AI-generated problems with hints and explanations rather than finding your own snippets, I built PyCodeIt for exactly this purpose. It is completely free, requires no account, and serves up a unique problem every session along with a full trace explanation.
Use it alongside LeetCode, not instead of it. The two skills are complementary. You want to be able to write solutions and read code with equal fluency. Most candidates can only do one.
Written by the developer behind PyCodeIt, a free AI-powered Python dry-run practice platform for technical interview preparation.
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