Python新手入门之四大基础语法速成指南

3my_name = "张三"        # 错误：以数字开头
my name = "李四"      # 错误：包含空格
class = "班级"        # 错误：class 是关键字

student_name = "小明"
age_in_years = 18

def calculate_total(price, tax):
    return price * (1 + tax)

x = 10
print(type(x))        # <class 'int'>

y = 3.14
print(type(y))        # <class 'float'>

z = "Hello"
print(type(z))        # <class 'str'>

# 类型转换
a = int("123")        # 字符串转整数
b = float("3.14")     # 字符串转浮点
c = str(100)          # 数字转字符串

round(number, ndigits)

print(round(3.14159))        # 输出：3
print(round(3.14159, 2))     # 输出：3.14
print(round(3.14159, 3))     # 输出：3.142
print(round(2.675, 2))       # 注意：输出可能是 2.67（因浮点精度问题）

# 传入多个参数
print(max(10, 20, 5))        # 输出：20

# 传入一个列表/元组
numbers = [3, 7, 2, 9, 1]
print(max(numbers))          # 输出：9

# 也可用于字符串（按字母顺序）
print(max("apple", "banana", "cherry"))  # 输出："cherry"

print(min(10, 20, 5))        # 输出：5

scores = [85, 92, 78, 96, 88]
print(min(scores))           # 输出：78

print(min("apple", "banana", "cherry"))  # 输出："apple"

s = "Python"

print(s[0])    # 输出：P
print(s[2])    # 输出：t
print(s[-1])   # 输出：n
print(s[-3])   # 输出：h

# 尝试越界会报错
# print(s[10])  # IndexError: string index out of range

string[start:end:step]

s = "Hello World"

print(s[0:5])    # 输出：Hello
print(s[6:11])   # 输出：World
print(s[6:])     # 从索引6到末尾 → World
print(s[:5])     # 从开头到索引5（不含）→ Hello

s = "Python"

print(s[-6:-3])  # 输出：Pyt（等价于 s[0:3]）
print(s[-3:])    # 输出：hon（从倒数第3个到末尾）

s = "abcdefgh"

print(s[::2])    # 每隔1个字符取1个 → aceg
print(s[1::2])   # 从索引1开始，每隔1个取1个 → bdfh
print(s[::-1])   # 反转字符串！→ hgfedcba

s = "Hi"
print(s[0:100])   # 输出：Hi（安全！）
print(s[10:20])   # 输出：""（空字符串）

first = "Hello"
second = "World"
result = first + " " + second
print(result)  # 输出：Hello World

name = "张三"
age = 25
# print("我叫" + name + "，今年" + age + "岁")  # ❌ 报错！
print("我叫" + name + "，今年" + str(age) + "岁")  # ✅ 正确

words = ["Python", "is", "awesome"]
sentence = " ".join(words)
print(sentence)  # 输出：Python is awesome

# 自定义分隔符
url_parts = ["https", "www.example.com", "home"]
full_url = "://".join(url_parts[:2]) + "/" + url_parts[2]
# 或更简洁地：
full_url = "/".join(["https:", "", "www.example.com", "home"])
print(full_url)  # 输出：https://www.example.com/home

text = "你好，Python！"
print(len(text))        # 输出：9（中文字符也占1位）

num = 42
print("数字是：" + str(num))  # 数字转字符串后拼接

print(ord('a'))         # 97
print(chr(97))          # a

s = "  \t Hello World \n "
print(repr(s.strip()))   # 输出：'Hello World'

data = "apple,banana,orange"
fruits = data.split(",")
print(fruits)  # ['apple', 'banana', 'orange']

path = "/home/user/docs"
parts = path.split("/")
print(parts)   # ['', 'home', 'user', 'docs']

print("Hello World!")
print(123)
print(3.14)
print(True)

print("姓名：", "张三", "年龄：", 20)
# 输出：姓名： 张三 年龄： 20

print("A", "B", "C", sep="-")         # 输出：A-B-C
print("Hello", end=" ")               # 不换行，输出后加空格
print("World")                        # 输出：Hello World

name = "小红"
age = 18
print(f"我叫{name}，今年{age}岁。")   # f-string（Python 3.6+）
print("我叫{}，今年{}岁。".format(name, age))  # format 方法

name = input("请输入你的名字：")
print("你好，" + name + "!")

age = input("请输入你的年龄：")
print("你明年将会是", int(age) + 1, "岁")

num1 = int(input("请输入第一个数字："))
num2 = int(input("请输入第二个数字："))
print("两数之和为：", num1 + num2)

a = eval(input("请输入一个表达式："))
print("输出结果为：", a)

eval(参数)