Python 基本語法
- main 主要描述程式的開始。就好比是 Java or C的 main
- 註解用 # 開頭
- 大小寫有區別
- function 用 def 開頭
- 每一行的空行是有特別意義的。因此，每段程式區塊的內縮必須一致!
[pastacode lang=”python” message=”Python main ” highlight=”” provider=”manual”]
# This is comments
def main():
print ("This is main function called")
b()
def b():
print (This is b function called)
if __name__== "__main__":
main()[/pastacode]
if ..else..
要注意的是 python 每個判斷式後面都有加上 :
if …else…每段程式的空格是必須的
[pastacode lang=”python” message=”Python if else” highlight=”” provider=”manual”]
# If .. else ..
def main():
a = 1
b = 2
if a < b:
print("a is less than b")
elif a > b:
print ("a is greater than b")
else:
print ("a is equal to b")
if __name__ == "__main__":
main()
[/pastacode]
[pastacode lang=”python” message=”Python if else” highlight=”” provider=”manual”]
def main():
a, b = 0, 1
if a < b:
print('a < b')
else:
print('a > b')
if __name__ == "__main__": main()[/pastacode]
function 定義
這個例子，主要定義一個 function ，印出 a-9的數字
[pastacode lang=”python” message=”Python function” highlight=”” provider=”manual”]
# This is comments
def main():
func(1)
func(6)
def func(a):
for i in range(a, 10):
print(i, end= ' ')
print()
if __name__== "__main__":
main()[/pastacode]
Object
python的世界內，所有的變數、函數、程式都是物件。
變數也是物件! 是的。每個物件都會有一個 id。物件會有一定的生命周期。
- imutable object: numbers, strings, tuples
- mutable object: lists, dictionaries,
舉例來說，在 python Shell 下執行
>>> x = 10
10
>>> type(x)
<Class ‘int’>
>>> id (x)
505401523
>>> x = 40
>>> id (x)
505409522
>>> x = 10
505401523
數字
[pastacode lang=”python” message=”Python number” highlight=”” provider=”manual”]
# This is comments
# the output will be
# <class 'int'> 1
# <class 'float'> 3.0
def main():
num1 = 1
num2 = 3.0
print(type(num1), num1)
print(type(num2), num2)
if __name__== "__main__":
main()[/pastacode]
字串
python 有十分強大的字串處理功能，
[pastacode lang=”python” message=”Python string” highlight=”” provider=”manual”]
def main():
n = 10
s = "this is {} string!".format(n)
print(s)
if __name__ =="__main__":
main()[/pastacode]
[pastacode lang=”python” message=”Python string” highlight=”” provider=”manual”]
# This is Python 2 syntax
def main():
n = 10
s = "this is %s string!" %n
print(s)
if __name__ =="__main__":
main()[/pastacode]
變數 – list
[pastacode lang=”python” message=”Python variable list” highlight=”” provider=”manual”]
def main():
x = 'string'
print(type(x),x[2:5])
print(type(x),x[3])
a = [1,2,3] # It's a list. List is mutable.
a.append(5) # we can use append or insert to change the value.
a.insert(0,7)
print(type(a),a)
if __name__ == "__main__": main()[/pastacode]
變數 – dictionary
python 獨特的變數， dictionary。
有些類似，可以自己建立自己的索引資料表。
例如，這個例子定義 one, two…five 每個元素的值
之後可以使用 sorted 的方式將 dictionary 定義的元素排序印出
[pastacode lang=”python” message=”Python dictionary” highlight=”” provider=”manual”]
def main():
dic = dict(
one = 1, two = 2, three = 3, four = 4, five = 'five'
)
for k in sorted(dic.keys()):
print(k, dic[k])
if __name__ == "__main__": main()[/pastacode]
迴圈
while
[pastacode lang=”python” message=”Python while” highlight=”” provider=”manual”]
# It's fibonacci
def main():
a, b = 0, 1
while b < 10:
print (b, end= ' ')
a, b = b, a + b
if __name__ == "__main__": main()[/pastacode]
利用for迴圈讀檔案
[pastacode lang=”python” message=”Python readfile” highlight=”” provider=”manual”]
def main():
f = open('readfile.txt')
for line in f.readlines():
print(line)
if __name__ == "__main__": main()[/pastacode]
搜尋一段字串
[pastacode lang=”python” message=”Python enumerate” highlight=”” provider=”manual”]
# search for the character t in the string
def main():
s = 'this is a testing string for enumeration'
for i, c in enumerate(s):
if c == 't': print ('index {} is an t').format(i))
if __name__ == "__main__": main()[/pastacode]