Python full stack development: Derivation of Python (list derivation, dictionary derivation, set deduction)

The derivation of comprehensions (also known as analytic) is a unique feature of Python. Derivation is the structure of another new data series that can be built from one data series.

• List-derived
• Dictionary (dict) derivation formula
• Set (set) derivation

List derivation one, use [] to generate list

Basic format

 for inch if the        condition]expression#  list generates an element expression, which can be a function with a return value.   the for in iterable    # Iteration iterable the item into expression expressions.  if condition    # Filters data based on conditions, generating desired data

Eg: List-generated

 for inch if Item% 2 = = 0]print(VAR)

# output
[0, 2, 4, 6, 8]      # Output as List

Second, use () to generate generator

Convert the list derivation [] to () to get the generator

Eg: generator expression

gen= ('egg%s'for inif i > 5) print (gen)
Print (List (gen))

# output
<generator object <genexpr> at 0x7f4b7c219d58>  # Builder Objects
[' Egg6 ', ' Egg7 ', ' Egg8 ', ' egg9 ']  # Data inside the generator　　

Dictionary derivation type

Dictionary derivation and list derivation are used in a similar way, except that the brackets should be changed to curly braces. Direct illustrative examples

Eg: uppercase and lowercase key merging

Mcase = {'a': 10,'b': 34,'A': 7,'Z': 3}mcase_frequency={k.lower (): Mcase.get (K.lower (), 0)+Mcase.get (K.upper (), 0) forKinchMcase.keys ()ifK.lower ()inch['a','b']}Printmcase_frequency#Output Results{' A ': +, ' B ':

Eg: Quick change of key and value

Mcase = {'a'b': in Mcase.items ()}print  mcase_frequency
# Output Results {ten: ' A ', ' C ': ' B '}

Set Deduction formula

is similar to the list derivation. The only difference is that it uses curly braces {}.

eg

 for inch [1, 1, 2]} Print (squared) # Output Results # Output:set ([1, 4])

Python full stack development: Derivation of Python (list derivation, dictionary derivation, set deduction)