输出：换行输出,不换行输出
e.g.:
print("hello")
print("hello",end="")
注释：单行注释 #,多行注释 """
e.g.:
#hello
"""
hello
"""
控制流：while,if,elseif,else:
e.g.:
x = 1
while True:
if x==10:
break
elif x==9:
print("We're getting close, on %d now!" % (x))
else:
print("x on %d now!" % (x))
x += 1
for i in 列表
e.g.:
for i in range(9,0,-1):
for j in range(9,i-1,-1):
print("%d*%d=%d\t"%(i,j,i*j),end = '')
print('')
