調用函數：
#!/usr/bin/env python3 # -*- coding: utf-8 -*- # 函數調用 >>> abs(100) 100 >>> abs(-110) 110 >>> abs(12.34) 12.34 >>> abs(1, 2) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: abs() takes exactly one argument (2 given) >>> abs('a') Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: bad operand type for abs(): 'str' >>> max(1, 2) 2 >>> max(2, 3, 1, -5) 3 >>> int('123') 123 >>> int(12.34) 12 >>> str(1.23) '1.23' >>> str(100) '100' >>> bool(1) True >>> bool('') False >>> a = abs # 變量a指向abs函數，相當于引用 >>> a(-1) # 所以也可以通過a調用abs函數 1 >>> n1 = 255 >>> n2 = 1000 >>> print(hex(n1)) 0xff >>> print(hex(n2)) 0x3e8 定義函數：
#!/usr/bin/env python3 # -*- coding: utf-8 -*- #函數定義 def myAbs(x): if x >= 0: return x else: return -x a = 10 myAbs(a) def nop(): # 空函數 pass
pass語句什么都不做 。
實際上pass可以用來作為占位符，比如現在還沒想好怎么寫函數代碼，就可以先寫一個pass，讓代碼運行起來。
if age >= 18: pass #缺少了pass，代碼就會有語法錯誤 >>> if age >= 18: ... File "<stdin>", line 2 ^ IndentationError: expected an indented block >>> myAbs(1, 2) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: myAbs() takes 1 positional argument but 2 were given >>> myAbs('A') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 2, in myAbs TypeError: unorderable types: str() >= int() >>> abs('A') Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: bad operand type for abs(): 'str' def myAbs(x): if not isinstance(x, (int, float)): raise TypeError('bad operand type') if x >= 0: return x else: return -x >>> myAbs('A') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 3, in myAbs TypeError: bad operand type
返回兩個值？
import math def move(x, y, step, angle = 0): nx = x + step * math.cos(angle) ny = y - step * math.sin(angle) return nx, ny >>> x, y = move(100, 100, 60, math.pi / 6) >>> print(x, y) 151.96152422706632 70.0
其實上面只是一種假象，Python函數返回的仍然是單一值 。
>>> r = move(100, 100, 60, math.pi / 6) >>> print(r) (151.96152422706632, 70.0)
實際上返回的是一個tuple！
但是，語法上，返回一個tuple可以省略括號， 而多個變量可以同時接受一個tuple，按位置賦給對應的值。
所以，Python的函數返回多值實際就是返回一個tuple，但是寫起來更方便。
函數執行完畢也沒有return語句時，自動return None。
練習 ：
import math def quadratic(a, b, c): x1 = (-b + math.sqrt(b * b - 4 * a * c)) / (2 * a) x2 = (-b - math.sqrt(b * b - 4 * a * c)) / (2 * a) return x1, x2 x1, x2 = quadratic(2, 5, 1) print(x1, x2) >>> import math >>> def quadratic(a, b, c): ... x1 = (-b + math.sqrt(b * b - 4 * a * c)) / (2 * a) ... x2 = (-b - math.sqrt(b * b - 4 * a * c)) / (2 * a) ... return x1, x2 ... >>> x1, x2 = quadratic(2, 5, 1) >>> print(x1, x2) -0.21922359359558485 -2.2807764064044154
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