When someone mentions the word self defense they usually think of traditional styles such as Karate. In the past martial arts were intimidating to others because they were relatively unknown and foreign.
Today things have changed significantly. Numerous traditional martial arts have been proven to be insufficient in a life threatening situation. Many have found out the hard way that learning some form of karate or Kung fu will not guarantee your safety and keep you from being attacked. What we have to realize is that all styles are not created equal, all self defense moves are not high percentage, and mastering a martial art will not make you invulnerable to attack. The reality is that anyone can be beaten in a physical confrontation despite their knowledge.
It is now more understood that the best self defense moves are those that involve your mind and are less of a physical nature. The main factor of surviving the streets is knowing your surroundings and knowing how to prevent an attack from happening. If your intuition tells you something seems dangerous or strange, pay attention. It's there to assist you in staying safe.
If you are a woman seeking to learn effective self defense moves to protect yourself from an attacker on the streets, I strongly recommend that you seek out a women's self defense program versus a traditional martial arts class. Karate classes are great in the respect that they strengthen your body physically, but unless you are training for a competition it is probably not going to be what you are looking for.
A basic women's self defense course will be fairly brief and simple so that you can absorb what is taught. It will be taught by a qualified instructor that will go over strategies on effective ways to avoid confrontation and how to escape life threatening situations quickly and effectively. Staying safe outside of your home doesn't mean you need to dedicate years to Kung fu training. It means you need to acquire some basic knowledge, a few highly effective techniques and learning to trust your intuition. If you take some time to learn this basic information then you can keep yourself safe by avoiding potentially dangerous situations.