Sự ảo ma của * trong Python

Thứ Năm, 05/01/2023

Tram Ho

Trong bài viết này, mình sẽ chém gió về một số cách sử dụng khác nhau của a.k.a “*” trong Python

Tạo collections với các phần tử lặp lại:

collections <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span> <span class="token operator">*</span> <span class="token number">2</span>
<span class="token keyword">print</span><span class="token punctuation">(</span>collections<span class="token punctuation">)</span>
<span class="token comment"># output: [1, 2, 3, 1, 2, 3]</span>

collections = [1, 2, 3] * 2

print(collections)

# output: [1, 2, 3, 1, 2, 3]

Chúng ta hoàn toàn có thể áp dụng tương tự với tuple hay chuỗi:

collections <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token number">2</span>
<span class="token keyword">print</span><span class="token punctuation">(</span>collections<span class="token punctuation">)</span>
<span class="token comment"># output: (1, 2, 3, 1, 2, 3)</span>

collections = (1, 2, 3) * 2

print(collections)

# output: (1, 2, 3, 1, 2, 3)

strings <span class="token operator">=</span> <span class="token string">"VN"</span> <span class="token operator">*</span> <span class="token number">2</span>
<span class="token keyword">print</span><span class="token punctuation">(</span>strings<span class="token punctuation">)</span>
<span class="token comment"># output: VNVN</span>

strings = "VN" * 2

print(strings)

# output: VNVN

Unpacking tập hợp tuần tự thành các biến riêng biệt

collections <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">)</span>
x<span class="token punctuation">,</span> y <span class="token operator">=</span> collections
<span class="token keyword">print</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span> y<span class="token punctuation">)</span>
<span class="token comment"># output: 4 5</span>

collections = (4, 5)

x, y = collections

print(x, y)

# output: 4 5

Với các biến mà ta không sử dụng ta có thể sử dụng _ để biểu diễn:

data <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token string">'VietNam'</span><span class="token punctuation">,</span> <span class="token number">84</span><span class="token punctuation">,</span> <span class="token number">100</span><span class="token punctuation">,</span> <span class="token string">'VN'</span><span class="token punctuation">]</span>
country<span class="token punctuation">,</span> country_code<span class="token punctuation">,</span> population<span class="token punctuation">,</span> short_name <span class="token operator">=</span> data
<span class="token keyword">print</span><span class="token punctuation">(</span>country<span class="token punctuation">,</span> country_code<span class="token punctuation">,</span> population<span class="token punctuation">,</span> short_name<span class="token punctuation">)</span>
<span class="token comment"># output: VietNam 84 100 VN</span>
country<span class="token punctuation">,</span> country_code<span class="token punctuation">,</span> population<span class="token punctuation">,</span> _ <span class="token operator">=</span> data
<span class="token keyword">print</span><span class="token punctuation">(</span>country<span class="token punctuation">,</span> country_code<span class="token punctuation">,</span> population<span class="token punctuation">)</span>
<span class="token comment"># output: VietNam 84 100</span>

data = ['VietNam', 84, 100, 'VN']

country, country_code, population, short_name = data

print(country, country_code, population, short_name)

# output: VietNam 84 100 VN

country, country_code, population, _ = data

# output: VietNam 84 100

Các tiêu đề sau mình xin mạn phép để tiếng anh vì dịch ra thì nghe nó cũng khá thô và cũng không sát nghĩa lắm :V

Unpacking Elements from Iterables of Arbitrary Length
Lấy tất cả các phần tử ở giữa của list:

grades <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">]</span>
first<span class="token punctuation">,</span> <span class="token operator">*</span>middle<span class="token punctuation">,</span> last <span class="token operator">=</span> grades
<span class="token keyword">print</span><span class="token punctuation">(</span>first<span class="token punctuation">,</span> middle<span class="token punctuation">,</span> last<span class="token punctuation">)</span>
<span class="token comment"># output: 1 [2, 3, 4] 5</span>

grades = [1, 2, 3, 4, 5]

first, *middle, last = grades

print(first, middle, last)

# output: 1 [2, 3, 4] 5

Lấy tất cả các phần tử còn lại của list:

record <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token string">'VN'</span><span class="token punctuation">,</span> <span class="token string">'vn@example.com'</span><span class="token punctuation">,</span> <span class="token string">'0773555121'</span><span class="token punctuation">,</span> <span class="token string">'0847555212'</span><span class="token punctuation">)</span>
name<span class="token punctuation">,</span> email<span class="token punctuation">,</span> <span class="token operator">*</span>phone_numbers <span class="token operator">=</span> record
<span class="token keyword">print</span><span class="token punctuation">(</span>name<span class="token punctuation">,</span> email<span class="token punctuation">,</span> phone_numbers<span class="token punctuation">)</span>
<span class="token comment"># output: VN vn@example.com ['0773555121', '0847555212']</span>

record = ('VN', 'vn@example.com', '0773555121', '0847555212')

name, email, *phone_numbers = record

print(name, email, phone_numbers)

# output: VN vn@example.com ['0773555121', '0847555212']

Dùng vài cái * một lúc nó sẽ như này:

record <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token string">'FUKADA'</span><span class="token punctuation">,</span> <span class="token number">50</span><span class="token punctuation">,</span> <span class="token number">123.45</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">,</span> <span class="token number">2012</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
name<span class="token punctuation">,</span> <span class="token operator">*</span>_<span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token operator">*</span>_<span class="token punctuation">,</span> year<span class="token punctuation">)</span> <span class="token operator">=</span> record
<span class="token keyword">print</span><span class="token punctuation">(</span>name<span class="token punctuation">,</span> year<span class="token punctuation">)</span>
<span class="token comment"># output: FUKADA 2012</span>

record = ('FUKADA', 50, 123.45, (12, 18, 2012))

name, *_, (*_, year) = record

print(name, year)

# output: FUKADA 2012

args and kwargs
Hãy thử xem hàm dưới đây:

<span class="token keyword">def</span> <span class="token function">calculate</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span>b<span class="token punctuation">,</span><span class="token operator">*</span>args<span class="token punctuation">,</span><span class="token operator">**</span>kwargs<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> b<span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span>arg<span class="token punctuation">)</span>
    <span class="token keyword">for</span> key <span class="token keyword">in</span> kwargs<span class="token punctuation">:</span>
        <span class="token keyword">print</span><span class="token punctuation">(</span>key<span class="token punctuation">,</span> kwargs<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">)</span>
calculate<span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> num1<span class="token operator">=</span><span class="token number">8</span><span class="token punctuation">,</span>num2<span class="token operator">=</span><span class="token number">9</span><span class="token punctuation">)</span>
<span class="token comment"># output: 2 3</span>
<span class="token comment"># (4, 5, 6)</span>
<span class="token comment"># num1 8</span>
<span class="token comment"># num2 9</span>

def calculate(a,b,*args,**kwargs):

print(a, b)

print(arg)

for key in kwargs:

print(key, kwargs[key])

calculate(2, 3, 4, 5, 6, num1=8,num2=9)

# output: 2 3

# (4, 5, 6)

# num1 8

# num2 9

Merging Different Types Of Iterables

var1 <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">)</span>
var2 <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">}</span>
collections <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token operator">*</span>var1<span class="token punctuation">,</span> <span class="token operator">*</span>var2<span class="token punctuation">]</span>
<span class="token keyword">print</span><span class="token punctuation">(</span>collections<span class="token punctuation">)</span>
<span class="token comment">#output: [1, 2, 3, 4, 5, 6]</span>

var1 = (1,2,3)

var2 = {4,5,6}

collections = [*var1, *var2]

print(collections)

#output: [1, 2, 3, 4, 5, 6]

Merging Two Dictionaries

dict1 <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token string">'key1'</span><span class="token punctuation">:</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token string">'key2'</span><span class="token punctuation">:</span><span class="token number">2</span><span class="token punctuation">}</span>
dict2 <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token string">'key3'</span><span class="token punctuation">:</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token string">'key4'</span><span class="token punctuation">:</span><span class="token number">4</span><span class="token punctuation">}</span>
<span class="token builtin">dict</span> <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token operator">**</span>dict1<span class="token punctuation">,</span> <span class="token operator">**</span>dict2<span class="token punctuation">}</span>
<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token builtin">dict</span><span class="token punctuation">)</span>
<span class="token comment">#output: {'key1': 1, 'key2': 2, 'key3': 3, 'key4': 4}</span>

dict1 = {'key1':1,'key2':2}

dict2 = {'key3':3,'key4':4}

dict = {**dict1, **dict2}

print(dict)

#output: {'key1': 1, 'key2': 2, 'key3': 3, 'key4': 4}

Chia sẻ bài viết ngay

Nguồn bài viết : Viblo

Sự ảo ma của * trong Python

TikTok trở thành nền tảng mảng xã hội lớn thứ hai ở Nam Phi

Mất giá nhanh nhất sau 9 tháng ra mắt, iPhone 14 Pro Max tiếp tục phá đáy tại Việt Nam

Hướng dẫn sử dụng ngôn ngữ R cho người mới bắt đầu

10 plugin cần thiết của SublimeText dành cho các lập trình viên JavaScript