Variables and assignment statements

Python 101

3.1 Introduction

In the cantilever beam example of Chapter 1, we began by creating the entire model in Abaqus/CAE. We then opened up a new file and ran a script which accomplished the exact same task. How exactly did the script work and what did all those code statements mean? Before we can start to analyze this, it is necessary to learn some basic Python syntax. If you have any programming experience at all, this chapter should be a breeze.

3.2 Statements

Python is written in the form of code statements as are other languages. However you do not need to put a semi-colon at the end of each statement. What the Python interpreter looks for are carriage returns (that’s when you press the ENTER key on the keyboard).

As long as you hit ENTER after each statement so that the next one is on a new line, the Python interpreter can tell where one statement ends and the other begins.

In addition statements within a code block need to be indented, such as statements inside a FOR loop. In languages such as C++ you use curly braces to signal the beginning and end of blocks of code whereas in Python you indent the code. Python is very serious about this, if you don’t indent code which is nested inside of something else (such as statements in a function definition or a loop) you will receive a lot of error messages.

Within a statement you can decide how much whitespace you wish to leave. So a=b+c can be written as a = b + c (notice the spaces between each character)

3.3 Variables and assignment statements

In some programming languages such as C++ and Java, variables are strongly typed. This means that you don’t just name a variable; you also declare a type for the variable. So for

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44 Python 101

 remove(y) – removes the first occurrence of y in the list

 pop(i) – removes the element at index [i] in the list, also returns it as the return value

Let’s work through an example.

Example 4.2 - Lists

In the ‘Kernel Command Line Interface’ tab of the lower panel of the window, type in the following statements hitting ENTER after each.

>>>random_stuff = ['car', 24, 'bird' , 78.5, 44, 'golf'] 

>>> print random_stuff[0] 

>>> print random_stuff[1] 

>>> print random_stuff 

>>> print len(random_stuff)   

>>> random_stuff.insert(2, ‘computer’) 

>>> print len(random_stuff) 

>>> print random_stuff 

>>> random_stuff.append(29) 

>>> print len(random_stuff) 

>>> print random_stuff 

>>> random_stuff.remove(24) 

>>> print random_stuff   

>>> removed_var = random_stuff.pop(2) 

>>> print removed_var 

>>> print random_stuff 

Your output will be as displayed the following figure. Note that the lowest index is 0, not 1, which is why random_stuff[0] refers to the first element ‘car’. The len() function returns the number of elements in the list. The append() function adds on whatever is passed to it as an argument to the end of the list. The remove() function removes the element that matches the argument you pass it. And the pop() function removes the element at the index position you pass it as an argument.

3.5 Dic

In document PythonScriptsForAbaqus_BookPreview (Page 50-55)