:= 海象运算符 Walrus Operator - Python Weekly EP2

Python3

// Author: Huahua

import re

import io

# Example 1:

a = [0] * 100

if len(a) > 10:

print(f"List is too long ({len(a)} elements, expected <= 10)")

n = len(a)

if n > 10:

print(f"List is too long ({n} elements, expected <= 10)")

if (x := len(a)) > 10:

print(f"List is too long ({x} elements, expected <= 10)")

# Example 2, bad

ads = "Now 20% off till 6/18"

m1 = re.search(r'(\d+)% off', ads)

discount1 = float(m1.group(1)) / 100 if m1 else 0.0

discount2 = float(m2.group(1)) / 100 if (m2 := re.search(r'(\d+)% off', ads)) else 0.0

print(f'{discount1 = }, {discount2 = }')

# Example 3

f1 = io.StringIO("123456789")

x1 = f1.read(4)

while x1 != '':

print(x1)

x1 = f1.read(4)

f2 = io.StringIO("123456789")

while (x2 := f2.read(4)) != '':

print(x2)

# Example 4

prog_langs = {'c++', 'python', 'java'}

langs = ['C++', 'Java', 'PYthon', 'English', '中文']

l1 = [lang.lower() for lang in langs if lang.lower() in prog_langs]

print(l1)

l2 = [l for lang in langs if (l := lang.lower()) in prog_langs]

print(l2)

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