Python List Comprehensions
PCAP objective 5.1 is build complex lists using list comprehensions. The syntax is an expression, a for, and an optional if, and once you can read those three parts in order the rest is practice. The examinable details are that there are four kinds of comprehension distinguished only by their brackets, that the loop variable does not survive the comprehension, and that a comprehension is the right fix for the [[0] * 2] * 3 trap.
Comprehensions and Lambdas Guide 20 of 25 Intermediate
- OSUbuntu 26.04 LTS
- Python3.14.4
- pip25.1.1
- TimeAbout 16 min
Comprehension variables have been scoped to the comprehension since Python 3.0 - in Python 2 they leaked into the enclosing scope. That is one of the differences on this page and older material gets it wrong.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| RUNNER01 | 192.168.0.27 | Ubuntu 26.04 LTS | Python 3.14.4 - the only machine this path needs | 2 Core | 4 GB | 50 GB |
This guide includes
Use this for the comprehension objective. This matters because the brackets decide what you get - the same expression gives a list, a set, a dictionary or a generator - and the loop variable does not leak out of any of them.
- replacing a loop with a comprehension
- using the three parts, and both kinds of
if - writing the other three comprehension types
- building a grid properly, without the repetition trap
- finding that the loop variable does not leak, and passing a comprehension straight into a built-in
Before you start
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The loop, and the comprehension that replaces it
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The three parts, and both kinds of if
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The other three comprehension types
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The grid, built properly this time
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The loop variable does not leak
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Comprehensions in the built-ins that consume them
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What the exam does with this objective