Files for python-cheatsheet, version 0.4.0; Filename, size File type Python version Upload date Hashes; Filename, size pythoncheatsheet-0.4.0-py2.py3-none-any.whl (7.4 kB) File type Wheel Python version py2.py3 Upload date Sep 29, 2018. R Reference Card 2.0 Public domain, v2.0 2012-12-24. V 2 by Matt Baggott, [email protected] V 1 by Tom Short, [email protected] Material from R for Beginners by permission of Emmanuel Paradis.
Cheatsheet 1 3 2 0 3
Thanks to Brendan O’Connor, this cheatsheet aims to be a quick reference of Scala syntactic constructions. Licensed by Brendan O’Connor under a CC-BY-SA 3.0 license. Dr antivirus pro 3 2 1000.
![Cheatsheet 1 3 2 0 Cheatsheet 1 3 2 0](https://storage.googleapis.com/molten/lava/2018/09/d84c3e64-numpy-cheat-sheet.jpg)
Cheatsheet 1 3 2 0t
variables | |
Good | Variable. |
Bad | Constant. |
Explicit type. | |
functions | |
Good Bad | Define function. Hidden error: without = it’s a procedure returning Unit ; causes havoc. Deprecated in Scala 2.13. |
Good Bad | Define function. Syntax error: need types for every arg. |
Type alias. | |
vs. | Call-by-value. Call-by-name (lazy parameters). |
Anonymous function. | |
vs. | Anonymous function: underscore is positionally matched arg. |
Anonymous function: to use an arg twice, have to name it. | |
Anonymous function: block style returns last expression. | |
Anonymous functions: pipeline style (or parens too). | |
Anonymous functions: to pass in multiple blocks, need outer parens. | |
Currying, obvious syntax. | |
Currying, obvious syntax. | |
Currying, sugar syntax. But then: | |
Need trailing underscore to get the partial, only for the sugar version. | |
Generic type. | |
Infix sugar. | |
Varargs. | |
packages | |
Wildcard import. | |
Selective import. | |
Renaming import. | |
Import all from java.util except Date . | |
At start of file: Packaging by scope: Package singleton: | Declare a package. |
data structures | |
Tuple literal (Tuple3 ). | |
Destructuring bind: tuple unpacking via pattern matching. | |
Bad | Hidden error: each assigned to the entire tuple. |
List (immutable). | |
Paren indexing (slides). | |
Cons. | |
same as | Range sugar. |
Empty parens is singleton value of the Unit type. Equivalent to void in C and Java. | |
control constructs | |
Conditional. | |
same as | Conditional sugar. |
While loop. | |
Do-while loop. | |
Break (slides). | |
same as | For-comprehension: filter/map. |
same as | For-comprehension: destructuring bind. |
same as | For-comprehension: cross product. |
For-comprehension: imperative-ish.sprintf style. | |
For-comprehension: iterate including the upper bound. | |
For-comprehension: iterate omitting the upper bound. | |
pattern matching | |
Good Bad | Use case in function args for pattern matching. |
Bad | v42 is interpreted as a name matching any Int value, and “42” is printed. |
Good | `v42` with backticks is interpreted as the existing val v42 , and “Not 42” is printed. |
Good | UppercaseVal is treated as an existing val, rather than a new pattern variable, because it starts with an uppercase letter. Thus, the value contained within UppercaseVal is checked against 3 , and “Not 42” is printed. |
object orientation | |
Constructor params - x is only available in class body. | |
Constructor params - automatic public member defined. | |
Constructor is class body. Declare a public member. Declare a gettable but not settable member. Declare a private member. Alternative constructor. | |
Anonymous class. | |
Define an abstract class (non-createable). | |
Define an inherited class. | |
Inheritance and constructor params (wishlist: automatically pass-up params by default). | |
Define a singleton (module-like). | |
Traits. Interfaces-with-implementation. No constructor params. mixin-able. | |
Multiple traits. | |
Must declare method overrides. | |
Create object. | |
Bad Good | Type error: abstract type. Instead, convention: callable factory shadowing the type. |
Class literal. | |
Type check (runtime). | |
Type cast (runtime). | |
Ascription (compile time). | |
options | |
Construct a non empty optional value. | |
The singleton empty optional value. | |
but | Null-safe optional value factory. |
same as | Explicit type for empty optional value. Factory for empty optional value. |
Pipeline style. | |
For-comprehension syntax. | |
same as | Apply a function on the optional value. |
same as | Same as map but function must return an optional value. |
same as | Extract nested option. |
same as | Apply a procedure on optional value. |
same as | Apply function on optional value, return default if empty. |
same as | Apply partial pattern match on optional value. |
same as | true if not empty. |
same as | true if empty. |
same as | true if not empty. |
same as | 0 if empty, otherwise 1 . |
same as | Evaluate and return alternate optional value if empty. |
same as | Evaluate and return default value if empty. |
same as | Return value, throw exception if empty. |
same as | Return value, null if empty. |
same as | Optional value satisfies predicate. |
same as | Optional value doesn't satisfy predicate. |
same as | Apply predicate on optional value or false if empty. |
same as | Apply predicate on optional value or true if empty. |
same as | Checks if value equals optional value or false if empty. |