6)控制结构之分支语句: 分支语句:if ... elif ... else 7)控制结构之循环语句: 循环语句有两种 : for循环 while循环 我们在后面的学习中会进一步不习; 以上介绍了python语言元素,并通过实例加深对python语法元素的理解,我们学习了以下语法元素:
if i in dic.keys(): dic[i]+=1 else: dic[i]=1 entropy=0 for i in dic: entropy+=solve(dic[i]/sum) entropy=-entropy return entropy with open('D:\\winter_python\\0119.csv') as f: f_csv=csv.DictReader(f) Chinese=[] Math=[] English=[] for row in f_csv: Chinese.append(...
deffind_first_even(numbers):result=None # 初始化变量fornuminnumbers:ifnum%2==0:result=numbreakreturnresultprint(find_first_even([1,3,5]))# 输出None,因为没有偶数 过程中的注意事项 明确变量作用域:理解Python中变量的作用域,确保在变量的作用域内使用前已经初始化。
(e.g., KeyboardInterrupt) if timeout is None: waiter.acquire() gotit = True else: if timeout > 0: gotit = waiter.acquire(True, timeout) else: gotit = waiter.acquire(False) return gotit finally: self._acquire_restore(saved_state) if not gotit: try: self._waiters.remove(waiter) ...
None if for lamdba continue True def from while nonlocal and del global not with as elif try or yield assert else import pass break except in raise Sentences or Lines x = 2 <---Assignment statement x = x + 2 <---Assignment with expression print(x) <---Print function...
解决方法:用global关键字来进行说明该变量是全局变量python代码: val=9 def test(flag): global val if flag: val = 1 else: print ‘test’ return val test(0) 2)局部变量,但仍然报出unboundLocal Error问题,比如: def test(flag): if (a): bbb = aaa elif(b): bbb2 = aaa2 print(bbb2) 错误...
sql_query 这个没有定义 你的代码导致的原因是 if result:_keys = ", ".join(escape(k) for k in result)_values = ", ".join(escapestr(result[k]) for k in result)sql_query = "REPLACE INTO %s (%s) VALUES (%s)" % (tablename, _keys, _values)else:print "无记录"这里执行...
()3536defstep(self):37new_val = (self.pb_val.get()+1)38ifnew_val>self.pb_max:39self.clear()40self.step()41else:42self.pb_val.set(new_val)43self.update_label()44454647classDualWork:48def__init__(self):49self.N1 = 550self.N2 = 751self.frm1 =PgBarFrm(root, self.N1)52self...
n)中，但是你写的函数dc1(n)却尝试去调用a。相当于a这个参数被越界调用了。改正：将a设置为全局变量。改正后的代码：a=1def dc(n):s=0def dc1(n):if a>=n:print(s)else:return dc2(n)def dc2(n):a=a+1return dc1(n)return dc1(n)在文件中更改为：...
if x is None: some_fallback_operation( ) else: some_operation(x) Discussion Python doesn’t have a specific function to test whether a variable is defined, since all variables are expected to have been defined before use, even if initially assigned the None object. Attempting to access a ...