共计 1678 个字符,预计需要花费 5 分钟才能阅读完成。
pip
蕴含模块所需的所有文件。
查看是否装置了 PIP
$ pip --version
装置 包
$ pip install package_name
应用包
import package_name
删除包
$ pip uninstall camelcase
列出包
pip list
Try Except
try:
print(x)
except:
print("An exception occurred")
您能够依据须要定义任意数量的异样块,例如,如果您想为非凡类型的谬误执行非凡代码块
try:
print(x)
except NameError:
print("Variable x is not defined")
except:
print("Something else went wrong")
如果没有引发谬误,能够应用 else 关键字定义要执行的代码块
try:
print("Hello")
except:
print("Something went wrong")
else:
print("Nothing went wrong")
如果指定了 finally 块,则无论 try 块是否引发谬误,都将执行 finally。
ry:
print(x)
except:
print("Something went wrong")
finally:
print("The'try except'is finished")
这对于敞开对象和清理资源十分有用
try:
f = open("demofile.txt")
try:
f.write("Lorum Ipsum")
except:
print("Something went wrong when writing to the file")
finally:
f.close()
except:
print("Something went wrong when opening the file")
作为 Python 开发人员,如果呈现条件,您能够抉择抛出异样。
x = -1
if x < 0:
raise Exception("Sorry, no numbers below zero")
您能够定义要引发的谬误类型,以及要打印给用户的文本。
x = "hello"
if not type(x) is int:
raise TypeError("Only integers are allowed")
用户输出
username = input("Enter username:")
print("Username is:" + username)
字符串格局
price = 49
txt = "The price is {} dollars"
print(txt.format(price)) # The price is 49 dollars
能够在花括号内增加参数,以指定如何转换值
price = 49
txt = "The price is {:.2f} dollars"
print(txt.format(price)) # The price is 49.00 dollars
如果要应用更多值,只需在 format()办法中增加更多值
quantity = 3
itemno = 567
price = 49
myorder = "I want {} pieces of item number {} for {:.2f} dollars."
print(myorder.format(quantity, itemno, price))
您能够应用索引号(大括号{0}内的数字)确保将值搁置在正确的占位符中
quantity = 3
itemno = 567
price = 49
myorder = "I want {0} pieces of item number {1} for {2:.2f} dollars."
print(myorder.format(quantity, itemno, price))
此外,如果要屡次援用同一值,请应用索引号
age = 36
name = "John"
txt = "His name is {1}. {1} is {0} years old."
print(txt.format(age, name))
命名索引
myorder = "I have a {carname}, it is a {model}."
print(myorder.format(carname = "Ford", model = "Mustang"))
正文完