title: keep decimal places when cast a float to a string in Python
body: <p>I'm writing an ATM program for school.  I've been doing a lot of research trying to figure out why when my numbers are like 100.00 they become 100.0 when cast as strings.  I've tried many different things but always get errors.</p>
  
  <pre><code>import sys
  
  #account balance
  acct_bal = float(500.25)
  deposit_amount = float(0.00)
  balance = float(0.00)
  withdrawal_amount = float(0.00)
  
  #&lt;--------functions go here--------------------&gt;
  #printbalance function, choice B
  def account_balance(acct_bal):
      print("Your current balance:")
      print(acct_bal)
  
  #deposit function, choice D
  def deposit(deposit_amount, balance):
      print("Deposit was $" + str(float(deposit_amount)) + ", current balance is $" + str(float(balance)))
      #print("Deposit was $" + "{:,.2f}".format(deposit_amount) + ", current balance is $" + "{:,.2f}".format(balance))
      #This one causes an error
      #Traceback (most recent call last):
      #File "G:/SNHU/1 - CURRENT/IT-140 Introduction to Scripting Python (10-30-17 to 12-24-17)/Module 5/ATM", line 29, in &lt;module&gt;
      #deposit(deposit_amount, balance)
      #File "G:/SNHU/1 - CURRENT/IT-140 Introduction to Scripting Python (10-30-17 to 12-24-17)/Module 5/ATM", line 17, in deposit
      #print("Deposit was $" + "{:,.2f}".format(deposit_amount) + ", current balance is $" + "{:,.2f}".format(balance))
      #ValueError: Unknown format code 'f' for object of type 'str'
  
  #withdraw function, choice W
  def withdrawal(withdrawal_amount, balance):
      print("Withdrawal amount was $" + str(float(withdrawal_amount)) + ", current balance is $" + str(float(balance)))
  
  #User Input goes here, use if/else conditional statement to call function based on user input
  userchoice = input("What would you like to do?\n")
  
  if (userchoice == "D"):
      deposit_amount = input("How much would you like to deposit today?\n")
      balance = acct_bal + float(deposit_amount)
      deposit(deposit_amount, balance)
  elif (userchoice == "B"):
      account_balance(acct_bal)
  else:
      withdrawal_amount = input("How much would you like to withdraw?\n")
      balance = acct_bal - float(withdrawal_amount)
      withdrawal(withdrawal_amount, balance)
  </code></pre>
  
  <p>This is the output I get:</p>
  
  <pre><code>What would you like to do?
  W
  How much would you like to withdraw?
  100
  Withdrawal amount was $100.0, current balance is $400.25
  </code></pre>
  
  <p>Should be ></p>
  
  <pre><code>Withdrawal amount was $100.00, current balance is $400.25
  </code></pre>
  
  <p>Process finished with exit code 0</p>