Init commit with many years of arduino sketches and projects. I dont know if the esp8266 includes much, but there are also libraries. I hope they dont have crazy automatic versioning through the Arduino IDE.

Projects/libraries/Installed_libs/Keypad/examples/CustomKeypad/CustomKeypad.ino

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+/* @file CustomKeypad.pde
+|| @version 1.0
+|| @author Alexander Brevig
+|| @contact alexanderbrevig@gmail.com
+||
+|| @description
+|| | Demonstrates changing the keypad size and key values.
+|| #
+*/
+#include <Keypad.h>
+
+const byte ROWS = 4; //four rows
+const byte COLS = 4; //four columns
+//define the cymbols on the buttons of the keypads
+char hexaKeys[ROWS][COLS] = {
+  {'0','1','2','3'},
+  {'4','5','6','7'},
+  {'8','9','A','B'},
+  {'C','D','E','F'}
+};
+byte rowPins[ROWS] = {3, 2, 1, 0}; //connect to the row pinouts of the keypad
+byte colPins[COLS] = {7, 6, 5, 4}; //connect to the column pinouts of the keypad
+
+//initialize an instance of class NewKeypad
+Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); 
+
+void setup(){
+  Serial.begin(9600);
+}
+  
+void loop(){
+  char customKey = customKeypad.getKey();
+  
+  if (customKey){
+    Serial.println(customKey);
+  }
+}