【Python】基础学习&技能提升&代码样例1：简单句式

官方教程

一、简单句式

1.1 数值

# 校验输入是否为有效数字
if not math.isnan(num):
	xxxx
# 浮点数精度问题	
print(0.1 + 0.2)   # 0.30000000000000004
0.1 + 0.1 + 0.1 == 0.3 # false
math.isclose(0.1 + 0.1 + 0.1, 0.3) # true
round(0.1 + 0.1 + 0.1, ndigits=2) == round(0.3, ndigits=2)  # true
# 字符串是否可转数字
st.isdecimal()
st.isnumeric()

# Generate a random number within the specified range
import random
random_number = random.uniform(min_range, max_range)
# Generate a random int in the range [min_val, max_val]
random_number = random.randint(min_val, max_val)
# 正负无穷大
a = float("inf")
b = float("-inf")

1.2字符串 string

# Reverse the string
reversed_string = input_string[::-1]
# Count occurrences of the target character
count = input_string.count(target_char)
# Check if main_string starts with search_string
starts_with = main_string.startswith(search_string)
# Trim the string
trimmed_string = string_with_spaces.strip()
# Check if main_string contains substring_to_check
contains_substring = substring_to_check in main_string
# Case-sensitive comparison
case_sensitive_comparison = string1 == string2
# Case-insensitive comparison
case_insensitive_comparison = string1.lower() == string2.lower()
# 移除所有白空格
import re
re.sub(r'\s', '', input_text)
# 判断字符串是否为空
len(string) == 0
# 字符串分割
st.split( );       # 以空格为分隔符，包含 \n
st.split(' ', 1 ); # 以空格为分隔符，分隔成两个
# Remove non-alphabetic characters and convert to lowercase 
clean_str1 = ''.join(filter(str.isalpha, str1.lower()))
# 格式
str_percentage = 'The user %s was born %s years ago.' % (name, age)
str_f_string = f'The user {
     name} was born {
     age} years ago.'
str_fun_string = 'The user {} was born {} years ago.'.format(txt, num)
str_fun_string2 = 'The user {1} was born {0} years ago.'.format(num, txt)
str_fun_string3 = 'The user {name} was born {age} years ago.'.format(name = txt, age = num)
print(f'PI is '{
   pi:.3}'.')   # number of digits (defaults n = number)
print(f'The user {
     name:>10} was born {
     age:>10} years ago.') # The user    Foo Bar was born      42.12 years ago.
print( f'a{
    {df{
     num}')  # 字符 { 要用 {
   {， 字符 }要用 }}
print(r'a\nb {name}') # a\nb {name}
print(rf'a\nb {
     name}') # a\nb foo

1.3 数组 list

# 快速构造数组
a1=[0]*4 # 错误，这是浅拷贝，见下几行解析
a1= [0 for _ in range(4)) # 可行，[0,0,0,0]
a1=list(itertools.repeat(0,4)) # 可行
 a3=[[0]*3 for _ in range(0,5)] #5行3列0
a1=list(itertools.repeat([0]*3,5))
## 误区-浅拷贝
>>> mat=[[0]*3]*3 
>>> mat
[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> mat[0][0]=1
>>> mat
[[1, 0, 0], [1, 0, 0], [1, 0, 0]]
# 反转数组
reversed_array  = original_array.copy().reverse()
reversed_array = original_array[::-1]
b = ['x', 2, 'y']
':'.join(b)    # 直接join会报错
':'.join( map(str, b) ) # 要先做类型转换
'ab:cd:ef'.split(':') # ['ab', 'cd', 'ef']
list('abcd')  # 字符串转数组，['a', 'b', 'c', 'd']
words = ['apple', 'banana', 'cat']
words.insert(2, 'zebra') # 指定位置插入，['apple', 'banana', 'zebra', 'cat']
words.remove('zebra') # 移除第一个匹配的元素
words.clear()