Python入门系列（九）pip、try except、用户输入、字符串格式

$ pip --version

$ pip install package_name

import package_name

$ pip uninstall camelcase

pip list

try:
  print(x)
except:
  print("An exception occurred")

try:
  print(x)
except NameError:
  print("Variable x is not defined")
except:
  print("Something else went wrong")

try:
  print("Hello")
except:
  print("Something went wrong")
else:
  print("Nothing went wrong")

ry:
  print(x)
except:
  print("Something went wrong")
finally:
  print("The 'try except' is finished")

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")

x = -1

if x < 0:
  raise Exception("Sorry, no numbers below zero")

x = "hello"

if not type(x) is int:
  raise TypeError("Only integers are allowed")

username = input("Enter username:")
print("Username is: " + username)

price = 49
txt = "The price is {} dollars"
print(txt.format(price)) # The price is 49 dollars

price = 49
txt = "The price is {:.2f} dollars"
print(txt.format(price)) # The price is 49.00 dollars

quantity = 3
itemno = 567
price = 49
myorder = "I want {} pieces of item number {} for {:.2f} dollars."
print(myorder.format(quantity, itemno, price))

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))

age = 36
name = "John"
txt = "His name is {1}. {1} is {0} years old."
print(txt.format(age, name))

myorder = "I have a {carname}, it is a {model}."
print(myorder.format(carname = "Ford", model = "Mustang"))