Lecture 9

Conditions, loops and files with Python

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if statement

We can use if statement to put conditions for parts of our code in Python. Logical conditions from math can be used as follows:

• x == y is for x is equal to y,
• x != y is for x is not equal to y,
• x > y is for x is greater than y,
• x < y is for x is less than y,
• x >= y is for x is greater than or equal to y,
• x <= y is for x is less than or equal to y,

An example script printing if variables X or Y are grater or less than or equal to 10 is below.

Here the important thing is that we need to put some spaces after the if statement line.

Two different if condition can be used together with/without and, or and not.

We can use elif or else as follows:

if can be used with arguments.

The other argument type action='store_true' is quite useful.

for loop

for loop is used for iterating over a sequence. See the script below.

Python can loop in the arrays as follows.

Multiple for loops can be used together.

while loop

while works as both for and if. Loop with a condition.

Writing files in Python

• "r" is used for reading,
• "w" is used for creating and writing (overwrite),
• "a" is used for creating and appending.

We can write strings with f.write method:

Write arrays into a file using NumPy. Text and binary files.

Read binary files.