Why Does Go\'s Map Iteration Order Change While Python\'s Dictionary Iteration Stays Consistent?

Why and How Go's Map Iteration Order Varies

In Go, maps are unordered collections of key-value pairs, where the order of elements is not guaranteed. This can lead to unexpected behavior when iterating over map objects. Below is a snippet that showcases this variability:

<code class="go">package main

import "fmt"

func main() {
    sample := map[string]string{
        "key1": "value1",
        "key2": "value2",
        "key3": "value3",
    }
    for i := 0; i < 3; i++ {
        fmt.Println(sample)
    }
}</code>

If you run this code, you will notice that the order of the printed keys varies with each iteration. This is because the language specification explicitly states:

"The iteration order over maps is not specified and is not guaranteed to be the same from one iteration to the next."

In contrast to Go, Python maintains a consistent iteration order for dictionaries, as demonstrated in the following Python snippet:

<code class="python"># Python requires specifying the encoding due to some challenges with Unicode processing
#!/bin/env python
#encoding=utf8

sample = {
    "key1": "value1",
    "key2": "value2",
    "key3": "value3",
}
for i in range(3):
    print(sample)</code>

Here, the iteration order remains consistent across all three iterations.

This difference stems from the fundamental design choices made by the language creators. Go prioritizes efficiency over determinism, while Python provides a stable iteration order. As a Go programmer, it is crucial to be aware of this inherent variability when working with maps.

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