Python 入門¶
事前須知¶
- 今天重點放在幫沒寫過程式的朋友們打基礎
- 碰到問題請馬上發問
- 歡迎隨時打斷 (如果有哪邊聽不懂，那一定是我跳太快，請馬上反應)
等等，Python 到底是啥啊？¶
Python 是一個由 Guido van Rossum 在 1991 年 2 月釋出的程式語言， 發展至今大約過了 20 餘年， 廣泛使用於科學計算、網頁後端開發、系統工具等地方。
Python 這名字是源自於當時 Guido van Rossum 在觀賞的 BBC 喜劇 「Monty Python's Flying Circus」。
[給稍微有經驗的程式設計師]
Python 主要的特性
- 強型別
- 物件導向
- 動態型別
- 直譯式
基本運算¶
In [1]:
1+2 # 加法
Out[1]:
3
In [2]:
3-4 # 減法
Out[2]:
-1
In [3]:
5*6 # 乘法
Out[3]:
30
In [4]:
7/8 # 除法
Out[4]:
0.875
In [5]:
7//8 # 除法，無條件捨去到個位數
Out[5]:
0
In [6]:
10%9 # 取餘數
Out[6]:
1
In [7]:
2 ** 10 # 指數
Out[7]:
1024
In [8]:
2 ** (1/2) # 開根號
Out[8]:
1.4142135623730951
In [9]:
1+2j # 複數 (這裡虛部用 j 表示)
Out[9]:
(1+2j)
In [10]:
(1+2j) * (3+4j) # 複數乘法
Out[10]:
(-5+10j)
In [11]:
2 ** (1+2j) # 複數指數
Out[11]:
(0.36691394948660344+1.9660554808224875j)
In [12]:
abs(-1) # absolute, 絕對值
Out[12]:
1
In [13]:
abs(1+2j) # absolute, 絕對值
Out[13]:
2.23606797749979
In [14]:
round(3.1415926, 3) # 四捨五入到小數點後第 3 位
Out[14]:
3.142
In [15]:
round(3.1415926, 4) # 四捨五入到小數點後第 4 位
Out[15]:
3.1416
賦值 (Assign)¶
用 = 來給名字
In [16]:
a = 1
b = 1.5
c = "asd"
In [17]:
type(42) # 用 type 可以得知型別
Out[17]:
int
In [18]:
type(3.14159265358979323846)
Out[18]:
float
In [19]:
"測試" # str, 字串
Out[19]:
'測試'
In [20]:
"""
我
是
多
行
字
串
""" # 用 3 個 " 夾起來
Out[20]:
'\n我\n是\n多\n行\n字\n串\n'
In [21]:
'''
我
是
多
行
字
串
''' # 也可以用 3 個 ' 夾起來
Out[21]:
'\n我\n是\n多\n行\n字\n串\n'
In [22]:
(42, 'O w O') # tuple, 可以放入各種東西的大箱子，放完後不能更動
Out[22]:
(42, 'O w O')
In [23]:
foo = (42, 'O w O')
foo[0] # subscript operator 可以取出其中的值
# 注意，index 從 0 開始算
Out[23]:
42
In [24]:
[42, 'O w O'] # list 和 tuple 相似，但放完後可以更動
Out[24]:
[42, 'O w O']
結構 (給比較有經驗的人)
In [25]:
{'a': 1, 'b': 42} # dict，冒號左邊的是 key、右邊的是 value，用 key 可以查到 value (想像查字典的狀況)
Out[25]:
{'a': 1, 'b': 42}
In [26]:
d = {'a': 1, 'b': 42}
d['b']
Out[26]:
42
結構
In [27]:
{1, 2, 3, 3, 3} # set，數學上的集合，裡面的東西不會重複，也沒有順序
Out[27]:
{1, 2, 3}
結構
In [28]:
A = {1, 2, 3}
B = {1, 2, 4}
A | B # 取聯集
Out[28]:
{1, 2, 3, 4}
In [29]:
A & B # 取交集
Out[29]:
{1, 2}
In [30]:
A ^ B # 取對稱差
Out[30]:
{3, 4}
In [31]:
A - B # 取差集
Out[31]:
{3}
In [32]:
dir(int) # 檢查可以使用的 method
Out[32]:
['__abs__', '__add__', '__and__', '__bool__', '__ceil__', '__class__', '__delattr__', '__dir__', '__divmod__', '__doc__', '__eq__', '__float__', '__floor__', '__floordiv__', '__format__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__init__', '__int__', '__invert__', '__le__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__round__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'bit_length', 'conjugate', 'denominator', 'from_bytes', 'imag', 'numerator', 'real', 'to_bytes']
In [33]:
help(int) # 看文件上的解說
Help on class int in module builtins:
class int(object)
| int(x=0) -> integer
| int(x, base=10) -> integer
|
| Convert a number or string to an integer, or return 0 if no arguments
| are given. If x is a number, return x.__int__(). For floating point
| numbers, this truncates towards zero.
|
| If x is not a number or if base is given, then x must be a string,
| bytes, or bytearray instance representing an integer literal in the
| given base. The literal can be preceded by '+' or '-' and be surrounded
| by whitespace. The base defaults to 10. Valid bases are 0 and 2-36.
| Base 0 means to interpret the base from the string as an integer literal.
| >>> int('0b100', base=0)
| 4
|
| Methods defined here:
|
| __abs__(self, /)
| abs(self)
|
| __add__(self, value, /)
| Return self+value.
|
| __and__(self, value, /)
| Return self&value.
|
| __bool__(self, /)
| self != 0
|
| __ceil__(...)
| Ceiling of an Integral returns itself.
|
| __divmod__(self, value, /)
| Return divmod(self, value).
|
| __eq__(self, value, /)
| Return self==value.
|
| __float__(self, /)
| float(self)
|
| __floor__(...)
| Flooring an Integral returns itself.
|
| __floordiv__(self, value, /)
| Return self//value.
|
| __format__(...)
|
| __ge__(self, value, /)
| Return self>=value.
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| __getnewargs__(...)
|
| __gt__(self, value, /)
| Return self>value.
|
| __hash__(self, /)
| Return hash(self).
|
| __index__(self, /)
| Return self converted to an integer, if self is suitable for use as an index into a list.
|
| __int__(self, /)
| int(self)
|
| __invert__(self, /)
| ~self
|
| __le__(self, value, /)
| Return self<=value.
|
| __lshift__(self, value, /)
| Return self<<value.
|
| __lt__(self, value, /)
| Return self<value.
|
| __mod__(self, value, /)
| Return self%value.
|
| __mul__(self, value, /)
| Return self*value.
|
| __ne__(self, value, /)
| Return self!=value.
|
| __neg__(self, /)
| -self
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| __or__(self, value, /)
| Return self|value.
|
| __pos__(self, /)
| +self
|
| __pow__(self, value, mod=None, /)
| Return pow(self, value, mod).
|
| __radd__(self, value, /)
| Return value+self.
|
| __rand__(self, value, /)
| Return value&self.
|
| __rdivmod__(self, value, /)
| Return divmod(value, self).
|
| __repr__(self, /)
| Return repr(self).
|
| __rfloordiv__(self, value, /)
| Return value//self.
|
| __rlshift__(self, value, /)
| Return value<<self.
|
| __rmod__(self, value, /)
| Return value%self.
|
| __rmul__(self, value, /)
| Return value*self.
|
| __ror__(self, value, /)
| Return value|self.
|
| __round__(...)
| Rounding an Integral returns itself.
| Rounding with an ndigits argument also returns an integer.
|
| __rpow__(self, value, mod=None, /)
| Return pow(value, self, mod).
|
| __rrshift__(self, value, /)
| Return value>>self.
|
| __rshift__(self, value, /)
| Return self>>value.
|
| __rsub__(self, value, /)
| Return value-self.
|
| __rtruediv__(self, value, /)
| Return value/self.
|
| __rxor__(self, value, /)
| Return value^self.
|
| __sizeof__(...)
| Returns size in memory, in bytes
|
| __str__(self, /)
| Return str(self).
|
| __sub__(self, value, /)
| Return self-value.
|
| __truediv__(self, value, /)
| Return self/value.
|
| __trunc__(...)
| Truncating an Integral returns itself.
|
| __xor__(self, value, /)
| Return self^value.
|
| bit_length(...)
| int.bit_length() -> int
|
| Number of bits necessary to represent self in binary.
| >>> bin(37)
| '0b100101'
| >>> (37).bit_length()
| 6
|
| conjugate(...)
| Returns self, the complex conjugate of any int.
|
| from_bytes(...) from builtins.type
| int.from_bytes(bytes, byteorder, *, signed=False) -> int
|
| Return the integer represented by the given array of bytes.
|
| The bytes argument must either support the buffer protocol or be an
| iterable object producing bytes. Bytes and bytearray are examples of
| built-in objects that support the buffer protocol.
|
| The byteorder argument determines the byte order used to represent the
| integer. If byteorder is 'big', the most significant byte is at the
| beginning of the byte array. If byteorder is 'little', the most
| significant byte is at the end of the byte array. To request the native
| byte order of the host system, use `sys.byteorder' as the byte order value.
|
| The signed keyword-only argument indicates whether two's complement is
| used to represent the integer.
|
| to_bytes(...)
| int.to_bytes(length, byteorder, *, signed=False) -> bytes
|
| Return an array of bytes representing an integer.
|
| The integer is represented using length bytes. An OverflowError is
| raised if the integer is not representable with the given number of
| bytes.
|
| The byteorder argument determines the byte order used to represent the
| integer. If byteorder is 'big', the most significant byte is at the
| beginning of the byte array. If byteorder is 'little', the most
| significant byte is at the end of the byte array. To request the native
| byte order of the host system, use `sys.byteorder' as the byte order value.
|
| The signed keyword-only argument determines whether two's complement is
| used to represent the integer. If signed is False and a negative integer
| is given, an OverflowError is raised.
|
| ----------------------------------------------------------------------
| Data descriptors defined here:
|
| denominator
| the denominator of a rational number in lowest terms
|
| imag
| the imaginary part of a complex number
|
| numerator
| the numerator of a rational number in lowest terms
|
| real
| the real part of a complex number
真偽值¶
- True/False
>>=<<===!=in- and/or/not
- is
- 各種 empty 狀況
- 0, 1
- "", "abc"
- (,), (1, 2)
- [], [1, 2]
- set(), {1, 2}
In [34]:
True
Out[34]:
True
In [35]:
False
Out[35]:
False
In [36]:
3 > 2
Out[36]:
True
In [37]:
5 <= 1
Out[37]:
False
In [38]:
1 != 2
Out[38]:
True
In [39]:
5 in [1, 2, 3, 4, 5]
Out[39]:
True
In [40]:
bool(0) # 用 bool 來看各個資料是 True 還是 False
Out[40]:
False
In [41]:
bool(42)
Out[41]:
True
In [42]:
bool(""), bool("abc")
Out[42]:
(False, True)
In [43]:
bool(tuple()), bool((1, 2))
Out[43]:
(False, True)
In [44]:
bool([]), bool([1, 2])
Out[44]:
(False, True)
In [45]:
bool(set()), bool({1, 2})
Out[45]:
(False, True)
In [46]:
bool(dict()), bool({'a': 1, 'b': 42})
Out[46]:
(False, True)
流程控制¶
- if ... elif ... else
- for ... in ...
- break
- continue
- while ... else ...
In [47]:
if 3 > 2:
print('Yes')
else:
print('Nooooooo, why can you come here?') # 如果 3 > 2 的話印出 'Yes'，否則印出 'Nooooooo, why can you come here?'
# 注意縮排是有影響的
Yes
In [48]:
if 2 > 3:
print('No')
elif 5 > 4:
print('Yes')
else:
print('@_@?') # 如果 2 > 3 的話印出 'No'，要不然 5 > 4 的話就印出 'Yes'，否則印出 '@_@?'
Yes
In [49]:
for i in [1, 2, 3, 4]: # i 會依序變成 1, 2, 3, 4 來執行下面 block 的程式，在這邊則是會被印出來
print(i)
1 2 3 4
In [50]:
for i in [1, 2, 3, 4]:
if i == 3:
break # 使用 break 來提早離開，當 i 變成 3 時就離開這個 for loop
print(i)
1 2
In [51]:
for i in [1, 2, 3, 4]:
print(i)
else:
print('End') # 如果前面的 for 成功跑完的話會執行這段
1 2 3 4 End
In [52]:
for i in [1, 2, 3, 4]:
if i == 3:
break
print(i)
else:
print('End') # 如果前面的 for 成功跑完的話會執行這段
1 2
In [53]:
for i in [1, 2, 3, 4]:
if i == 3:
continue # continue 可以跳過這次後面的 code，進入下一輪
print(i)
else:
print('End') # 如果前面的 for 成功跑完的話會執行這段
1 2 4 End
In [54]:
i = 4
while i > 0: # 當 while 後面接的條件一直符合時就會繼續執行
print(i)
i = i - 1
4 3 2 1
In [55]:
i = 4
while i > 0: # 當 while 後面接的條件一直符合時就會繼續執行
print(i)
i = i - 1
else:
print('End')
4 3 2 1 End
In [56]:
i = 4
while i > 0: # 當 while 後面接的條件一直符合時就會繼續執行
if i == 3:
break
print(i)
i = i - 1
else:
print('End')
4
更多字串操作¶
- string formatting
- 字串串接
- slice :
start:stop[:step]
In [57]:
'{} | {}'.format(1, 2) # 用 {} 表示要留著填空，後面用 .format 傳入要填進去的值
Out[57]:
'1 | 2'
In [58]:
'~ {} ~'.format([1, 2, 3, 4])
Out[58]:
'~ [1, 2, 3, 4] ~'
In [59]:
'上上下下' + '左右左右' + 'BA' # 用 + 可以把字串接起來
Out[59]:
'上上下下左右左右BA'
In [60]:
s = 'abcdefghijklmnopqrstuvwxyz'
In [61]:
s[0]
Out[61]:
'a'
In [62]:
s[1:4] # index 1 到 index 3 (index 4 結束)
Out[62]:
'bcd'
In [63]:
s[-1] # 負的 index 會倒回去
Out[63]:
'z'
In [64]:
s[1:8:2] # index 1 到 index 7，每次跳兩步
Out[64]:
'bdfh'
In [65]:
s[-1:-9:-2]
Out[65]:
'zxvt'
In [66]:
s[::-1] # 不指定的話會自動帶入值
Out[66]:
'zyxwvutsrqponmlkjihgfedcba'
Function¶
一些常用的 code 會寫成 function，之後要使用時直接呼叫就可以了
In [67]:
def hello(): # 用 def 定義一個 function 叫作 hello，負責輸出 'Hello ~'
print('Hello ~')
hello() # 呼叫
Hello ~
In [68]:
def f_42():
return 42 # 用 return 來回傳資料
x = f_42()
print(x)
42
In [69]:
def f(a, b=3): # a 和 b 是參數，b 預設是 3
return a+b
x = f(10)
y = f(10, 5)
print(x, y)
13 15
總複習¶
- 認識 Python
- 基本運算
- 加減乘除
- 取餘數
- 指數
- 複數
- 除法，無條件捨去到個位數 (//)
- 絕對值 (abs)
- 四捨五入 (round)
- 型別
- 基本型別
- int
- float
- str
"'"""'''\escape
- tuple
- list
- dict
- set
|&^
- 基本型別
- 輔助工具
- dir
- help
- type
- 賦值 (Assign)
- 真偽值
- True/False
>>=<<===!=in- and/or/not
- is
- 各種 empty 狀況
- 0, 1
- "", "abc"
- (,), (1, 2)
- [], [1, 2]
- set(), {1, 2}
- 流程控制 (注意冒號和縮排)
- if ... elif ... else
- for ... in ...
- break
- continue
- while ... else ...
- 更多字串操作
- format string
- 字串串接
- slice :
start:stop[:step]
- function
- def
- return
- arguments
- defaults
- function call
- Slice
- slice(start, stop[, step])
- a[0], a[-1], a[1:99:3], a[-1:-11:-2], a[::-1] (不打的話就自動帶入頭尾), range(-1, -11, -2)
其他還有很多還沒包含的議題 (未全部列出)¶
Python 內建 features¶
- method
- list.pop, list.remove, list.append
- ...
- 轉型別
- str(123)
- 打包
***
- module
- import ...
- from ... import ...
- class
- method
- list comprehension
- lambda function
- 內建函數 (builtins)
- len
- sum
- count
- 三元運算子
- 生成器 (generator / yield)
- 例外事件處理 (try-except)
- 函數裝飾 (decorator)
- metaprogramming
- 更多字串操作
- string encoding/decoding
- Python 3 和 Python 2 的差異
Python - 科學運算¶
SciPy¶
- NumPy - 矩陣相關操作
- Matplotlib - plotting
- SymPy - symbolic mathematics
- Pandas - Python Data Analysis Library
- Scikits
網頁開發¶
- Django
- Flask
額外資訊¶
Python 實作¶
[名詞解釋]
- "Python" 指的是程式語言的規範
- "CPython" 是官方 "Python" 直譯器實作的名稱
CPython¶
Python 官方實作，核心部份使用 C 語言撰寫，部份 Standard Library 使用 Python 撰寫，對於 Python 的支援最完整。
PyPy¶
利用 JIT (just-in-time compiler) 技術加速 Python 程式的專案，目標是要相容於 CPython 的同時大幅提升效能。
[更多訊息]
PyPy 是用 RPython framework 撰寫的 Python interpreter，RPython 是一個 Python 的子集，RPython 限制了一些比較動態的 feature， 藉此可以做 type inference，之後再做分析、優化，並生出 Tracing JIT、Garbage Collector。
Jython¶
Java 版的 Python 實作，可以把 Python code 轉成 Java bytecode 在 JVM (Java Virtual Machine) 執行，除此之外可以 import Java 的 class
IronPython¶
利用 .NET framework 實作的 Python，可以使用 .NET framework 的 libraries