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David Beazley
2020-05-28 17:41:59 -05:00
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Notes/07_Advanced_Topics/02_Anonymous_function.md
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@@ -1,3 +1,5 @@
[Contents](../Contents) \| [Previous (7.1 Variable Arguments)](01_Variable_arguments) \| [Next (7.3 Returning Functions)](03_Returning_functions)
# 7.2 Anonymous Functions and Lambda
### List Sorting Revisited
@@ -30,7 +32,9 @@ It seems simple enough. However, how do we sort a list of dicts?
By what criteria?
You can guide the sorting by using a *key function*. The *key function* is a function that receives the dictionary and returns the value in a specific key.
You can guide the sorting by using a *key function*. The *key
function* is a function that receives the dictionary and returns the
value of interest for sorting.
```python
def stock_name(s):
@@ -39,7 +43,7 @@ def stock_name(s):
portfolio.sort(key=stock_name)
```
The value returned by the *key function* determines the sorting.
Here's the result.
```python
# Check how the dictionaries are sorted by the `name` key
@@ -56,13 +60,16 @@ The value returned by the *key function* determines the sorting.
### Callback Functions
Callback functions are often short one-line functions that are only used for that one operation. For example of previous sorting example.
Programmers often ask for a short-cut, so is there a shorter way to specify custom processing for `sort()`?
In the above example, the key function is an example of a callback
function. The `sort()` method "calls back" to a function you supply.
Callback functions are often short one-line functions that are only
used for that one operation. Programmers often ask for a short-cut
for specifying this extra processing.
### Lambda: Anonymous Functions
Use a lambda instead of creating the function.
In our previous sorting example.
Use a lambda instead of creating the function. In our previous
sorting example.
```python
portfolio.sort(key=lambda s: s['name'])
@@ -156,6 +163,6 @@ Try sorting the portfolio according to the price of each stock
Note: `lambda` is a useful shortcut because it allows you to
define a special processing function directly in the call to `sort()` as
opposed to having to define a separate function first (as in part a).
opposed to having to define a separate function first.
[Contents](../Contents) \| [Previous (7.1 Variable Arguments)](01_Variable_arguments) \| [Next (7.3 Returning Functions)](03_Returning_functions)