Building a Hierarchical Calculator Application with PyQt5
Interface Layout Implement a layered display using a read-only QTextEdit as the background canvas with two QLabel components for data presentation. Position the primary value label at the lower portion and the expression history label at the upper right to mimic modern calculator aesthetics.
self.display_panel = QtWidgets.QTextEdit(self.main_container)
self.display_panel.setGeometry(QtCore.QRect(40, 30, 431, 111))
self.display_panel.setReadOnly(True)
self.active_operand = QtWidgets.QLabel(self.main_container)
self.active_operand.setGeometry(QtCore.QRect(40, 90, 431, 51))
font = QtGui.QFont()
font.setPointSize(20)
font.setBold(True)
self.active_operand.setFont(font)
self.active_operand.setAlignment(QtCore.Qt.AlignRight | QtCore.Qt.AlignVCenter)
self.expression_preview = QtWidgets.QLabel(self.main_container)
self.expression_preview.setGeometry(QtCore.QRect(200, 30, 271, 61))
self.expression_preview.setFont(QtGui.QFont("Arial", 13))
self.expression_preview.setAlignment(QtCore.Qt.AlignRight | QtCore.Qt.AlignVCenter)
Input Handling Consolidate digit entry through a single method that manages string concatenation and state validation. This eliminates redundant functions for individual numbers while handling edge cases like multiple decimal points or leading zeros.
def append_character(self, char):
current_text = self.active_operand.text()
if char == '.' and '.' in current_text:
return
if current_text == '0' and char != '.':
current_text = ''
self.active_operand.setText(current_text + char)
Cascading Operation Logic Implement a deferred execution model where each operation triggers the computation of the previous pending operation. Store the accumulator and pending operator as instance variables rather than relying solely on UI text extraction.
def trigger_operation(self, operator):
current_value = float(self.active_operand.text())
if self.pending_operator is None:
self.accumulator = current_value
else:
self.accumulator = self.compute(self.pending_operator, self.accumulator, current_value)
self.pending_operator = operator
self.expression_preview.setText(f"{self.accumulator} {operator}")
self.active_operand.clear()
def compute(self, op, left, right):
if op == '+': return left + right
if op == '-': return left - right
if op == '*': return left * right
if op == '/': return left / right if right != 0 else 0
This approach ensures that 8 + 4 * 2 evaluates sequentially as (8 + 4) * 2 rather than following standard precedence rules, matching the behavior of basic electronic calculators.
