Issue #11661 has been updated by Nobuyoshi Nakada.

Tracker changed from Feature to Bug
Backport set to 2.0.0: REQUIRED, 2.1: REQUIRED, 2.2: REQUIRED

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Bug #11661: sprintf causes a KeyError instead of using a default value for hash substitution
https://bugs.ruby-lang.org/issues/11661#change-54800

* Author: Eddy Luten
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* ruby -v: 
* Backport: 2.0.0: REQUIRED, 2.1: REQUIRED, 2.2: REQUIRED
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When using a format string that substitutes hash values (or using the `%` operator on a string), instead of using the Hash's default value if a key is not present, it causes a KeyError.

As an end-user, to get around this, my hash needs to know about all the possible keys ahead of time and pre-assign a value to them or handle the KeyError. Logically, I would assume that the `sprintf` implementation would use the default Hash value.

I wanted to open this issue to see what your collective thoughts were on this since I have a fork running locally that fixes this issue and was wondering if I could send a patch/PR for this.

This issue is reproducible using the following code:

```ruby
my_hash = Hash.new('world')
puts "hello %{location}" % my_hash # expecting "hello world"
# "KeyError: key{location} not found"
```



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