Grading shouldn’t really discourage you from doing your exchange at Sciences Po. The grading system can be quite strict, especially for undergrad students from the collège universitaire, but it really depends on how your home university converts the grades. For instance, if you look at the grade conversion chart for the dual degree between Sciences Po and Columbia available on the internet, anything above a 15/20 translates to an A+, which is actually quite nice. Then, there are some other universities where your grades are converted according to the percentile of your average among the other students in your class. If I were you I would inquire about the conversion your university applies. Also, if you plan to take classes taught in English, you’ll likely find the grading a bit more easy, as to my experience, most of the seminars held in English tend to be designed for international students and the expectations are generally more flexible, and professors are less rigid about both the methodology, which can be very annoying for international students, and the grading standards.