input: Write a python function to fetch weather data and extract the temperature from the OpenWeather API.
  assert fetch_weather_data('New York') > -100  # Assuming the temperature will never be below -100 F
  assert fetch_weather_data('Los Angeles') > -100
  assert fetch_weather_data('Tokyo') > -100
output: import requests
  
  def fetch_weather_data(city):
      api_key = 'your_api_key_here'  # Replace with your actual API key
      base_url = 'http://api.openweathermap.org/data/2.5/weather?'
      complete_url = f"{base_url}q={city}&appid={api_key}&units=imperial"  # 'units=imperial' for Fahrenheit
      
      response = requests.get(complete_url)
      data = response.json()
      
      if data["cod"] != "404":
          main = data["main"]
          temperature = main["temp"]
          return temperature
      else:
          return None