A lambda is an anonymous inline function, useful when a short function must be passed directly to another function or stored as a value. section 9.6 section 9.10
Use the compact form when the operation is simple:
- Write lambda, followed by parameters, a colon, and one expression: lambda parameter1, parameter2: expression. section 9.6
- Omit return; the expression's value is returned automatically. section 9.6
- Pass the function inline when a named definition would add unnecessary separation, such as a sort key. section 5.4.1
- Store lambdas in data structures when a small operation belongs alongside related values. section 9.6
Sort words by length
Given word_list = ['Python', 'is', 'better', 'than', 'C'], use word_list.sort(key=lambda x: len(x)). The result is ['C', 'is', 'than', 'Python', 'better']. For descending order, prefer sort(reverse=True) or reverse after a standard sort rather than using a custom sort key. section 5.4.1
t2 = {'FtoK': lambda deg_f: 273.15 + (deg_f - 32) * 5 / 9,
'CtoK': lambda deg_c: 273.15 + deg_c} #1
t2['FtoK'](32)
273.15
#1 lambda functions as dictionary values
A dictionary can keep conversion operations in one place: t2['FtoK'](32) evaluates a lambda stored under the FtoK key. section 9.6
